Geometry-based priority for the construction of candidate lists

ABSTRACT

In one example, a device includes a memory configured to store the video data; and one or more processors implemented in circuitry and configured to determine a plurality of distances between a first representative point of a current block of video data and a plurality of second representative points of neighboring blocks to the current block, add one or more of the neighboring blocks as candidates to a candidate list of the current block in an order according to the distances between the first representative point and the second representative points, and code the current block using the candidate list. The candidate list may be, for example, a merge list, an AMVP list, or a most probable mode list. Alternatively, the candidate list may be a list of candidates from which to determine context information for context-adaptive binary arithmetic coding (CABAC).

This application claims the benefit of U.S. Provisional Application No.62/384,089, filed Sep. 6, 2016, the entire contents of which are herebyincorporated by reference.

TECHNICAL FIELD

This disclosure relates to video coding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), ITU-T H.265, also referred to as High Efficiency VideoCoding (HEVC), and extensions of such standards. The video devices maytransmit, receive, encode, decode, and/or store digital videoinformation more efficiently by implementing such video codingtechniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video frame or a portion of a video frame) may bepartitioned into video blocks, which for some techniques may also bereferred to as treeblocks, coding units (CUs) and/or coding nodes. Videoblocks in an intra-coded (I) slice of a picture are encoded usingspatial prediction with respect to reference samples in neighboringblocks in the same picture. Video blocks in an inter-coded (P or B)slice of a picture may use spatial prediction with respect to referencesamples in neighboring blocks in the same picture or temporal predictionwith respect to reference samples in other reference pictures. Picturesmay be referred to as frames, and reference pictures may be referred toa reference frames.

Spatial or temporal prediction results in a predictive block for a blockto be coded. Residual data represents pixel differences between theoriginal block to be coded and the predictive block. An inter-codedblock is encoded according to a motion vector that points to a block ofreference samples forming the predictive block, and the residual dataindicating the difference between the coded block and the predictiveblock. An intra-coded block is encoded according to an intra-coding modeand the residual data. For further compression, the residual data may betransformed from the pixel domain to a transform domain, resulting inresidual transform coefficients, which then may be quantized. Thequantized transform coefficients, initially arranged in atwo-dimensional array, may be scanned in order to produce aone-dimensional vector of transform coefficients, and entropy coding maybe applied to achieve even more compression.

SUMMARY

In general, this disclosure describes techniques related to constructionof candidate lists. Candidate lists may be constructed for various videocoding techniques, such as signaling of intra-prediction modes, motioninformation coding (e.g., in merge mode or advanced motion vectorprediction (AMVP) mode), or other such video coding techniques. Thisdisclosure describes geometry-based priority for construction ofcandidate lists. In some aspects, geometry information, e.g., distancesbetween the current block and the neighboring blocks, may be used todetermine the priority or insertion order of candidates for theconstruction of candidate lists.

In one example, a method of coding video data includes determining aplurality of distances between a first representative point of a currentblock of video data and a plurality of second representative points ofneighboring blocks to the current block, adding one or more of theneighboring blocks as candidates to a candidate list of the currentblock in an order according to the distances between the firstrepresentative point and the second representative points, and codingthe current block using the candidate list.

In another example, a device for coding video data includes a memoryconfigured to store the video data; and one or more processorsimplemented in circuitry and configured to determine a plurality ofdistances between a first representative point of a current block ofvideo data and a plurality of second representative points ofneighboring blocks to the current block, add one or more of theneighboring blocks as candidates to a candidate list of the currentblock in an order according to the distances between the firstrepresentative point and the second representative points, and code thecurrent block using the candidate list.

In another example, a device for coding video data includes means fordetermining a plurality of distances between a first representativepoint of a current block of video data and a plurality of secondrepresentative points of neighboring blocks to the current block, meansfor adding one or more of the neighboring blocks as candidates to acandidate list of the current block in an order according to thedistances between the first representative point and the secondrepresentative points, and means for coding the current block using thecandidate list.

In another example, a computer-readable storage medium having storedthereon instructions that, when executed, cause a processor to determinea plurality of distances between a first representative point of acurrent block of video data and a plurality of second representativepoints of neighboring blocks to the current block, add one or more ofthe neighboring blocks as candidates to a candidate list of the currentblock in an order according to the distances between the firstrepresentative point and the second representative points, and code thecurrent block using the candidate list.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating spatial neighboringcandidates in High Efficiency Video Coding (HEVC).

FIG. 2 is a conceptual diagram illustrating temporal motion vectorprediction (TMVP) in HEVC.

FIG. 3 is a conceptual diagram illustrating an example predictionstructure for 3D-HEVC.

FIG. 4 is a conceptual diagram illustrating sub-PU based inter-viewmotion prediction in 3D-HEVC.

FIG. 5 is a conceptual diagram illustrating sub-PU motion predictionfrom a reference picture.

FIG. 6 is a conceptual diagram illustrating relevant pictures in ATMVP(similar to TMVP).

FIG. 7 is a flowchart showing an example method according to thetechniques of this disclosure.

FIG. 8 is a conceptual diagram showing one example of a PU andneighboring blocks.

FIG. 9 is a conceptual diagram showing another example of a PU andneighboring blocks.

FIG. 10 is a conceptual diagram showing another example of a PU andneighboring blocks.

FIG. 11 is a conceptual diagram showing another example of a PU andneighboring blocks.

FIG. 12 is a conceptual diagram illustrating an example of geometricinformation of spatial merging candidates according to techniques ofthis disclosure.

FIG. 13 is a conceptual diagram illustrating an example of geometricinformation of spatial merging candidates according to techniques ofthis disclosure.

FIG. 14 is a block diagram illustrating an example video encoding anddecoding system that may be configured to perform the techniques of thisdisclosure.

FIG. 15 is a block diagram illustrating an example of video encoder thatmay be configured to perform the techniques of this disclosure.

FIG. 16 is a block diagram illustrating an example of video decoder thatmay be configured to perform the techniques of this disclosure.

FIG. 17 is a flowchart illustrating an example method of encoding videodata according to the techniques of this disclosure.

FIG. 18 is a flowchart illustrating an example method of decoding videodata in accordance with the techniques of this disclosure.

DETAILED DESCRIPTION

This disclosure describes techniques that may be used to improve theconstruction of candidate lists and context modeling in video codecs byintroducing a priority based on geometry information between the currentblock and the neighboring blocks to determine the priority or insertionorder for the construction of candidate lists such as the mergingcandidate list, AMVP list and intra MPM list. Moreover, this geometryinformation can be used for the determination of the context for CABACcoding. The order of multiple candidates (such as merging candidate,most probable intra mode candidate) may be adaptively determined by thegeometry priority. It may be used in the context of advanced videocodecs, such as extensions of HEVC or the next generation of videocoding standards.

Video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-TH.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual andITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its ScalableVideo Coding (SVC) and Multiview Video Coding (MVC) extensions. Thelatest joint draft of MVC is described in “Advanced video coding forgeneric audiovisual services,” ITU-T Recommendation H.264, March 2010.

In addition, there is a newly developed video coding standard, namelyHigh Efficiency Video Coding (HEVC), developed by the JointCollaboration Team on Video Coding (JCT-VC) of ITU-T Video CodingExperts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG).The latest HEVC draft specification, and referred to as HEVC WDhereinafter, is available fromphenix.int-evry.fr/jct/doc_end_user/documents/14_Vienna/wg11/JCTVC-N1003-v1.zip.The HEVC standard has been finalized in G. J. Sullivan; J.-R. Ohm; W.-J.Han; T. Wiegand (December 2012). “Overview of the High Efficiency VideoCoding (HEVC) Standard” (PDF). IEEE Transactions on Circuits and Systemsfor Video Technology (IEEE) 22 (12).

ITU-T VCEG (Q6/16) and ISO/IEC MPEG (JTC 1/SC 29/WG 11) are now studyingthe potential need for standardization of future video coding technologywith a compression capability that significantly exceeds that of thecurrent HEVC standard (including its current extensions and near-termextensions for screen content coding and high-dynamic-range coding). Thegroups are working together on this exploration activity in a jointcollaboration effort known as the Joint Video Exploration Team (JVET) toevaluate compression technology designs proposed by their experts inthis area. The JVET first met during 19-21 Oct. 2015. And the latestversion of reference software, i.e., Joint Exploration Model 3 (JEM 3)could be downloaded from: jvet.hhi.fraunhofer.de/svn/svnHMJEMSoftware/tags/HM-16.6-JEM-3.0/. The algorithm description for JEM3is described in J. Chen, E. Alshina, G. J. Sullivan, J.-R. Ohm, J. Boyce“Algorithm description of Joint Exploration Test Model 3”, JVET-C1001,San Diego, March 2016.

For each block, a set of motion information can be available. The set ofmotion information contains motion information for forward and backwardprediction directions. Here forward and backward prediction directionsare two prediction directions corresponding to reference picture list 0(RefPicList0) and reference picture list 1 (RefPicList1) of a currentpicture or slice. The terms “forward” and “backward” do not necessarilyhave a geometry meaning. Instead, they are used to distinguish whichreference picture list a motion vector is based on. Forward predictionmeans the prediction formed based on reference list 0, while backwardprediction means the prediction formed based on reference list 1. Incase both reference list 0 and reference list 1 are used to form aprediction for a given block, it is called bi-directional prediction.

For a given picture or slice, if only one reference picture list isused, every block inside the picture or slice is forward predicted. Ifboth reference picture lists are used for a given picture or slice, ablock inside the picture or slice may be forward predicted, or backwardpredicted, or bi-directionally predicted.

For each prediction direction, the motion information contains areference index and a motion vector. A reference index is used toidentify a reference picture in the corresponding reference picture list(e.g., RefPicList0 or RefPicList1). A motion vector has both ahorizontal and a vertical component, with each indicating an offsetvalue along horizontal and vertical direction respectively. In somedescriptions, for simplicity, the word of “motion vector” may be usedinterchangeably with motion information, to indicate both the motionvector and its associated reference index.

Picture order count (POC) is widely used in video coding standards toidentify a display order of a picture. Although there are cases twopictures within one coded video sequence may have the same POC value, ittypically doesn't happen within a coded video sequence. When multiplecoded video sequences are present in a bitstream, pictures with a samevalue of POC may be closer to each other in terms of decoding order.

POC values of pictures are typically used for reference picture listconstruction, derivation of reference picture set as in HEVC and motionvector scaling.

In Wiegand, Thomas; Sullivan, Gary J.; Bjøntegaard, Gisle; Luthra, Ajay(July 2003), “Overview of the H.264/AVC Video Coding Standard” (PDF).IEEE Transactions on Circuits and Systems for Video Technology 13 (7),H.264/AVC (Advanced Video Coding), each inter macroblock (MB) may bepartitioned into four different ways:

-   -   One 16×16 MB partition    -   Two 16×8 MB partitions    -   Two 8×16 MB partitions    -   Four 8×8 MB partitions

Different MB partitions in one MB may have different reference indexvalues for each direction (RefPicList0 or RefPicList1). When an MB isnot partitioned into four 8×8 MB partitions, it has only one motionvector for each MB partition in each direction. When an MB ispartitioned into four 8×8 MB partitions, each 8×8 MB partition can befurther partitioned into sub-blocks, each of which can have a differentmotion vector in each direction. There are four different ways to getsub-blocks from an 8×8 MB partition:

-   -   One 8×8 sub-block    -   Two 8×4 sub-blocks    -   Two 4×8 sub-blocks    -   Four 4×4 sub-blocks

Each sub-block can have a different motion vector in each direction.Therefore, motion vector is present in a level equal to higher thansub-block.

In AVC, temporal direct mode could be enabled in either MB or MBpartition level for skip or direct mode in B slices. For each MBpartition, the motion vectors of the block co-located with the currentMB partition in the RefPicList1[0] of the current block are used toderive the motion vectors. Each motion vector in the co-located block isscaled based on POC distances.

In AVC, a spatial direct mode can also be used to predict motioninformation from the spatial neighbors.

In HEVC, the largest coding unit in a slice is called a coding treeblock (CTB) or coding tree unit (CTU). A CTB contains a quad-tree, thenodes of which are coding units (CUs).

The size of a CTB can be ranges from 16×16 to 64×64 in the HEVC mainprofile (although technically 8×8 CTB sizes can be supported). A codingunit (CU) could be the same size of a CTB although and as small as 8×8.Each coding unit is coded with one mode. When a CU is inter coded, itmay be further partitioned into 2 or 4 prediction units (PUs) or becomejust one PU when further partition doesn't apply. When two PUs arepresent in one CU, they can be half size rectangles or two rectanglesize with ¼ or ¾ size of the CU.

When the CU is inter coded, one set of motion information is present foreach PU. In addition, each PU is coded with a unique inter-predictionmode to derive the set of motion information.

In the HEVC standard, there are two inter prediction modes, named merge(skip is considered as a special case of merge) and advanced motionvector prediction (AMVP) modes respectively for a prediction unit (PU).

In either AMVP or merge mode, a motion vector (MV) candidate list ismaintained for multiple motion vector predictors. The motion vector(s),as well as reference indices in the merge mode, of the current PU aregenerated by taking one candidate from the MV candidate list.

The MV candidate list contains up to 5 candidates for the merge mode andonly two candidates for the AMVP mode. A merge candidate may contain aset of motion information, e.g., motion vectors corresponding to bothreference picture lists (list 0 and list 1) and the reference indices.If a merge candidate is identified by a merge index, the referencepictures are used for the prediction of the current blocks, as well asthe associated motion vectors are determined. However, under AMVP modefor each potential prediction direction from either list 0 or list 1, areference index needs to be explicitly signaled, together with an MVPindex to the MV candidate list since the AMVP candidate contains only amotion vector. In AMVP mode, the predicted motion vectors can be furtherrefined.

As can be seen above, a merge candidate corresponds to a full set ofmotion information while an AMVP candidate contains just one motionvector for a specific prediction direction and reference index. That is,in general, motion information includes a motion vector predictor, areference picture list, an index into the reference picture list, and inthe case of AMVP, differences to be applied to the motion vectorpredictor. According to HEVC, in merge mode, the motion vector,reference picture list, and index are inherited from a selectedcandidate, whereas in AMVP, the motion vector predictor corresponds tothe motion vector of a selected candidate, and the reference picturelist, index, and motion vector difference values are signaled.

The candidates for both modes are derived similarly from the samespatial and temporal neighboring blocks.

FIG. 1 is a conceptual diagram illustrating spatial neighboringcandidates in HEVC. Spatial MV candidates are derived from theneighboring blocks shown on FIG. 1, for a specific PU (PU₀), althoughthe methods generating the candidates from the blocks differ for mergeand AMVP modes.

In merge mode, up to four spatial MV candidates can be derived with theorders showed on FIG. 1 (a) with numbers, and the order is thefollowing: left (0, A1), above (1, B1), above right (2, B0), below left(3, A0), and above left (4, B2), as shown in FIG. 1 (a).

In merge mode, up to four spatial MV candidates can be derived with theorders shown in FIG. 1(a) with numbers, and the order is the following:left (0, A1), above (1, B1), above-right (2, B0), below-left (3, A0),and above left (4, B2), as shown in FIG. 1 (a). That is, in FIG. 4(a),block 100 includes PU0 104A and PU1 104B. When a video coder (e.g., avideo encoder or a video decoder) is to code (encode or decode) motioninformation for PU0 104A using merge mode, the video coder adds motioninformation from spatial neighboring blocks 108A, 108B, 108C, 108D, and108E to a candidate list, in that order. Blocks 108A, 108B, 108C, 108D,and 108E may also be referred to as, respectively, blocks A1, B1, B0,A0, and B2, as in HEVC.

In AVMP mode, the neighboring blocks are divided into two groups: a leftgroup including blocks 0 and 1, and an above group including blocks 2,3, and 4 as shown on FIG. 1 (b). These blocks are labeled, respectively,as blocks 110A, 110B, 110C, 110D, and 110E in FIG. 1(b). In particular,in FIG. 1(b), block 102 includes PU0 106A and PU1 106B, and blocks 110A,110B, 110C, 110D, and 110E represent spatial neighbors to PU0 106A. Foreach group, the potential candidate in a neighboring block referring tothe same reference picture as that indicated by the signaled referenceindex has the highest priority to be chosen to form a final candidate ofthe group. It is possible that all neighboring blocks do not contain amotion vector pointing to the same reference picture. Therefore, if sucha candidate cannot be found, the first available candidate will bescaled to form the final candidate; thus, the temporal distancedifferences can be compensated.

FIG. 2 is a conceptual diagram illustrating temporal motion vectorprediction in HEVC. In particular, FIG. 2(a) illustrates an example CU120 including PU0 122A and PU 1 122B. PU0 122A includes a center block126 for PU 122A and a bottom-right block 124 to PU0 122A. FIG. 2(a) alsoshows an external block 128 for which motion information may bepredicted from motion information of PU0 122A, as discussed below. FIG.2(b) illustrates a current picture 130 including a current block 138 forwhich motion information is to be predicted. In particular, FIG. 2(b)illustrates a collocated picture 134 to current picture 130 (includingcollocated block 140 to current block 138), a current reference picture132, and a collocated reference picture 136. Collocated block 140 ispredicted using motion vector 144, which is used as a temporal motionvector predictor (TMVP) 142 for motion information of block 138.

A video coder may add a TMVP candidate (e.g., TMVP candidate 142) intothe MV candidate list after any spatial motion vector candidates if TMVPis enabled and the TMVP candidate is available. The process of motionvector derivation for the TMVP candidate is the same for both merge andAMVP modes. However, the target reference index for the TMVP candidatein the merge mode is set to 0, according to HEVC.

The primary block location for the TMVP candidate derivation is thebottom right block outside of the collocated PU, as shown in FIG. 2 (a)as block 124 to PU0 122A, to compensate the bias to the above and leftblocks used to generate spatial neighboring candidates. However, ifblock 124 is located outside of the current CTB row or motioninformation is not available for block 124, the block is substitutedwith center block 126 of the PU as shown in FIG. 2(a).

The motion vector for TMVP candidate 142 is derived from co-locatedblock 140 of co-located picture 134, as indicated in slice levelinformation. The motion vector for the co-located PU is calledcollocated MV.

Similar to temporal direct mode in AVC, a motion vector of the TMVPcandidate may be subject to motion vector scaling, which is performed tocompensate picture order count (POC) distance differences and/ortemporal distance distances between current picture 130 and currentreference picture 132, and collocated picture 134 and collocatedreference picture 136. That is, motion vector 144 may be scaled toproduce TMVP candidate 142, based on these POC/temporal distancedifferences.

Several aspects of merge and AMVP modes are worth mentioning as follows.

Motion vector scaling: It is assumed that the value of motion vectors isproportional to the distance of pictures in the presentation time. Amotion vector associates two pictures, the reference picture, and thepicture containing the motion vector (namely the containing picture).When a motion vector is utilized to predict the other motion vector, thedistance of the containing picture and the reference picture iscalculated based on the Picture Order Count (POC) values.

For a motion vector to be predicted, both its associated containingpicture and reference picture may be different. Therefore a new distance(based on POC) is calculated. And the motion vector is scaled based onthese two POC distances. For a spatial neighboring candidate, thecontaining pictures for the two motion vectors are the same, while thereference pictures are different. In HEVC, motion vector scaling appliesto both TMVP and AMVP for spatial and temporal neighboring candidates.

Artificial motion vector candidate generation: If a motion vectorcandidate list is not complete, artificial motion vector candidates aregenerated and inserted at the end of the list until it will have allcandidates.

In merge mode, there are two types of artificial MV candidates: combinedcandidate derived only for B-slices and zero candidates used only forAMVP if the first type doesn't provide enough artificial candidates.

For each pair of candidates that are already in the candidate list andhave necessary motion information, bi-directional combined motion vectorcandidates are derived by a combination of the motion vector of thefirst candidate referring to a picture in the list 0 and the motionvector of a second candidate referring to a picture in the list 1.

Pruning process for candidate insertion: Candidates from differentblocks may happen to be the same, which decreases the efficiency of amerge/AMVP candidate list. A pruning process is applied to solve thisproblem. It compares one candidate against the others in the currentcandidate list to avoid inserting identical candidate in certain extent.To reduce the complexity, only limited numbers of pruning process isapplied instead of comparing each potential one with all the otherexisting ones.

FIG. 3 illustrates an example prediction structure for 3D-HEVC. 3D-HEVCis a 3D video extension of HEVC under development by JCT-3V. 3D-HEVC isdescribed in Gerhard Tech; Krzysztof Wegner; Ying Chen; Sehoon Yea (Feb.18, 2015). “3D-HEVC Draft Text 7,” JCT-3V. Certain techniques related tothe techniques of this disclosure are described with respect to FIGS. 3and 4 below.

FIG. 3 shows a multiview prediction structure for a three-view case. V3denotes the base view and a picture in a non-base view (V1 or V5) can bepredicted from pictures in a dependent (base) view of the same timeinstance.

It is worth mentioning that the inter-view sample prediction (fromreconstructed samples) is supported in MV-HEVC, a typical predictionstructure of which is shown in FIG. 3.

Both MV-HEVC and 3D-HEVC are compatible to HEVC in a way that the base(texture) view is decodable by HEVC (version 1) decoder.

In MV-HEVC, a current picture in a non-base view may be predicted byboth pictures in the same view and pictures in a reference view of thesame time instance, by putting all of these pictures in referencepicture lists of the picture. Therefore, a reference picture list of thecurrent picture contains both temporal reference pictures and inter-viewreference pictures.

A motion vector associated with a reference index corresponding to atemporal reference picture is denoted as a temporal motion vector.

A motion vector associated with a reference index corresponding to aninter-view reference picture is denoted as a disparity motion vector.

3D-HEVC supports all features in MV-HEVC. Therefore, inter-view sampleprediction as mentioned above is enabled.

In addition, more advanced texture only coding tools and depthrelated/dependent coding tools are supported.

The texture-only coding tools often require the identification of thecorresponding blocks (between views) that may belong to the same object.Therefore, disparity vector derivation is a basic technology in 3D-HEVC.

Inter-view sample prediction (from reconstructed samples) is supportedin MV-HEVC, a typical prediction structure of which is shown in FIG. 5.

FIG. 4 is a conceptual diagram illustrating sub-PU based inter-viewmotion prediction in 3D-HEVC. FIG. 4 shows current picture 160 of acurrent view (V1) and a collocated picture 162 in a reference view (V0).Current picture 160 includes a current PU 164 including four sub-Pus166A-166D (sub-PUs 166). Respective disparity vectors 174A-174D(disparity vectors 174) identify corresponding sub-PUs 168A-168D tosub-PUs 166 in collocated picture 162. In 3D-HEVC, a sub-PU levelinter-view motion prediction method for the inter-view merge candidate,i.e., the candidate derived from a reference block in the referenceview.

When such a mode is enabled, current PU 164 may correspond to areference area (with the same size as current PU identified by thedisparity vector) in the reference view and the reference area may havericher motion information than needed for generation one set of motioninformation typically for a PU. Therefore, a sub-PU level inter-viewmotion prediction (SPIVMP) method may be used, as shown in FIG. 4.

This mode may also be signaled as a special merge candidate. Each of thesub-PUs contains a full set of motion information. Therefore, a PU maycontain multiple sets of motion information.

Similarly, in depth coding of 3D-HEVC, it is designed that the MotionParameter Inheritance (MPI) candidate derived from texture view can alsobe extended in a way similar to sub-PU level inter-view motionprediction.

For example, if the current depth PU has a co-located region whichcontains multiple PUs, the current depth PU may be separated intosub-PUs, each may have a different set of motion information.

This method is called sub-PU MPI.

Example sub-PU related techniques for 2D video coding are described inU.S. application Ser. No. 14/497,128, the entirety of which isincorporated by reference herein. In U.S. application Ser. No.14/497,128, a sub-PU based advanced TMVP (ATMVP) design has beenproposed.

In single-layer coding, a two-stage advanced temporal motion vectorprediction design is proposed. The first stage is utilized to derive avector identifying the corresponding block of the current predictionunit (PU) in a reference picture and a second stage is to extractmultiple sets motion information from the corresponding block and assignthem to sub-PUs of the PU. Each sub-PU of the PU therefore is motioncompensated separately. The concept of the ATMVP is summarized asfollows: (1) The vector in the first stage can be derived from spatialand temporal neighboring blocks of the current PU. (2) This process maybe achieved as activating a merge candidate among all the other mergecandidates.

Applicable to single-layer coding and sub-PU temporal motion vectorprediction, a PU or CU may have motion refinement data to be conveyed ontop of the predictors.

Several design aspects of U.S. application Ser. No. 14/497,128 arehighlighted as follows:

1. The first stage of vector derivation can also be simplified by just azero vector.2. The first stage of vector derivation may include identifying jointlythe motion vector and its associated picture. Various ways of selectingthe associated picture and further deciding the motion vector to be thefirst stage vector have been proposed.3. If the motion information during the above process is unavailable,the “first stage vector” is used for substitution.4. A motion vector identified from a temporal neighbor has to be scaledto be used for the current sub-PU, in a way similar to motion vectorscaling in TMVP. However, which reference picture such a motion vectormay be scaled to can be designed with one of the following ways:

-   -   a. The picture is identified by a fixed reference index of the        current picture.    -   b. The picture is identified to be the reference picture of the        corresponding temporal neighbor, if also available in a        reference picture list of the current picture.    -   c. The picture is set to be the co-located picture identified in        the first stage and from where the motion vectors are grabbed        from.

To address some design issues in U.S. application Ser. No. 14/497,128,the following techniques were proposed in U.S. application Ser. No.15/005,564, the entire content of which is incorporated by referenceherein:

-   -   1. Position of the ATMVP candidate, if inserted, e.g., as a        merge candidate list        -   a. Assume the spatial candidates and TMVP candidate are            inserted into a merge candidate list in a certain order. The            ATMVP candidate may be inserted in any relatively fixed            position of those candidates.            -   i. In one alternative, for example, the ATMVP candidate                can be inserted in the merge candidate list after the                first two spatial candidates e.g., A1 and B1;            -   ii. In one alternative, for example, the ATMVP candidate                can be inserted after the first three spatial candidates                e.g., A1 and B1 and B0;            -   iii. In one alternative, for example, the ATMVP                candidate can be inserted after the first four                candidates e.g., A1, B1, B0, and A0.            -   iv. In one alternative, for example, the ATMVP candidate                can be inserted right before the TMVP candidate.            -   v. In one alternatively, for example, the ATMVP                candidate can be inserted right after the TMVP                candidate.        -   b. Alternatively, the position of ATMVP candidate in the            candidate list can be signaled in the bitstream. The            positions of other candidates, including the TMVP candidate            can be additionally signaled.    -   2. Availability check of the ATMVP candidate can apply by        accessing just one set of motion information. When such set of        information is unavailable, e.g., one block being intra-coded,        the whole ATMVP candidate is considered as unavailable. In that        case, the ATMVP will not be inserted into the merge list.        -   a. A center position or a center sub-PU is used purely to            check the availability of the ATMVP candidate. When a center            sub-PU is used, the center sub-PU is chosen to be the one            that covers the center position (e.g., the center 3            position, with a relative coordinate of (W/2, H/2) to the            top-left sample of the PU, wherein W×H is the size of the            PU). Such a position or center sub-PU may be used together            with the temporal vector to identify a corresponding block            in the motion source picture. A set of motion information            from the block that covers the center position of a            corresponding block is identified.    -   3. Representative set of motion information for the ATMVP coded        PU from a sub-PU.        -   a. To form the ATMVP candidate the representative set of            motion information is first formed.        -   b. Such a representative set of motion information may be            derived from a fixed position or fixed sub-PU. It can be            chosen in the same way as that of the set of motion            information used to determine the availability of the ATMVP            candidate, as described in bullet #2.        -   c. When a sub-PU has identified its own set of motion            information and is unavailable, it is set to be equal to the            representative set of motion information.        -   d. If the representative set of motion information is set to            be that of a sub-PU, no additional motion storage is needed            at the decoder side for the current CTU or slice in the            worst case scenario.        -   e. Such a representative set of motion information is used            in all scenarios when the decoding processes requires the            whole PU to be represented by one set of motion information,            including pruning, such that the process is used to generate            combined bi-predictive merging candidates.    -   4. The ATMVP candidate is pruned with TMVP candidate and        interactions between TMVP and ATMVP can be considered; detailed        techniques are listed below:        -   a. The pruning of a sub-PU based candidate, e.g., ATMVP            candidate with a normal candidate, may be conducted by using            the representative set of motion information (as in bullet            #3) for such a sub-PU based candidate. If such set of motion            information is the same as a normal merge candidate, the two            candidates are considered as the same.        -   b. Alternatively, in addition, a check is performed to            determine whether the ATMVP contains multiple different sets            of motion information for multiple sub-Pus; if at least two            different sets are identified, the sub-PU based candidate is            not used for pruning, i.e., is considered to be different to            any other candidate; Otherwise, it may be used for pruning            (e.g., may be pruned during the pruning process).        -   c. Alternatively, in addition, the ATMVP candidate may be            pruned with the spatial candidates, e.g., the left and top            ones only, with positions denoted as A1 and B1.        -   d. Alternatively, only one candidate is formed from temporal            reference, being either ATMVP candidate or TMVP candidate.            When ATMVP is available, the candidate is ATMVP; otherwise,            the candidate is TMVP. Such a candidate is inserted into the            merge candidate list in a position similar to the position            of TMVP. In this case, the maximum number of candidates may            be kept as unchanged.            -   i. Alternatively, TMVP is always disabled even when                ATMVP is unavailable.            -   ii. Alternatively, TMVP is used only when ATMVP is                unavailable.        -   e. Alternatively, when ATMVP is available and TMVP is            unavailable, one set of motion information of one sub-PU is            used as the TMVP candidate. In this case, furthermore, the            pruning process between ATMVP and TMVP is not applied.        -   f. Alternatively, or additionally, the temporal vector used            for ATMVP may be also used for TMVP, such that the            bottom-right position or center 3 position as used for            current TMVP in HEVC do not need to be used.            -   i. Alternatively, the position identified by the                temporal vector and the bottom-right and center 3                positions are jointly considered to provide an available                TMVP candidate.    -   5. Multiple availability checks for ATMVP are supported to give        higher chances for the ATMVP candidate to be more accurate and        efficient. When the current ATMVP candidate from the motion        source picture as identified by the first temporal vector (e.g.,        as shown in FIG. 9) is unavailable, other pictures can be        considered as motion source picture. When another picture is        considered, it may be associated with a different second        temporal vector, or may be associated simply with a second        temporal vector scaled from the first temporal vector that        points to the unavailable ATMVP candidate.        -   a. A second temporal vector can identify an ATMVP candidate            in a second motion source picture and the same availability            check can apply. If the ATMVP candidate as derived from the            second motion source picture is available, the ATMVP            candidate is derived and no other pictures need to be            checked; otherwise, other pictures as motion source pictures            need to be checked.        -   b. Pictures to be checked may be those in the reference            picture lists of the current picture, with a given order.            For each list, the pictures are checked in the ascending            order of the reference index. List X is first checked and            pictures in list Y (being 1−X) follows.            -   i. List X is chosen so that list X is the list that                contains the co-located picture used for TMVP.            -   ii. Alternatively, X is simply set to be 1 or 0.        -   c. Pictures to be checked are those identified by motion            vectors of the spatial neighbors, with a given order.    -   6. A partition of the PU that the current ATMVP apply to may be        2N×2N, N×N, 2N×N, N×2N or asymmetric motion partition (AMP)        partitions, such as 2N×N/2.        -   a. Alternatively, in addition, if other partition sizes can            be allowed, ATMVP can be supported too, and such a size may            include e.g., 64×8.        -   b. Alternatively, the mode may be only applied to certain            partitions, e.g., 2N×2N.    -   7. The ATMVP candidate is marked as a different type of merge        candidate.    -   8. When identifying a vector (temporal vector as in the first        stage) from neighbors, multiple neighboring positions, e.g.,        those used in merge candidate list construction, can be checked        in order. For each of the neighbors, the motion vectors        corresponding to reference picture list 0 (list 0) or reference        picture list 1 (list 1) can be checked in order. When two motion        vectors are available, the motion vectors in list X can be        checked first and followed by list Y (with Y being equal to        1−X), so that list X is the list that contains the co-located        picture used for TMVP. In ATMVP, a temporal vector is used be        added as a shift of any center position of a sub-PU, wherein the        components of temporal vector may need to be shifted to integer        numbers. Such a shifted center position is used to identify a        smallest unit that motion vectors can be allocated to, e.g.,        with a size of 4×4 that covers the current center position.        -   a. Alternatively, motion vectors corresponding to list 0 may            be checked before those corresponding to list 1;        -   b. Alternatively, motion vectors corresponding to list 1 may            be checked before those corresponding to list 0;        -   c. Alternatively, all motion vectors corresponding to list X            in all spatial neighbors are checked in order, followed by            the motion vectors corresponding to list Y (with Y being            equal to 1−X). Here, list “X” can be the list that indicates            where co-located picture belongs, or just simply set to be 0            or 1.        -   d. The order of the spatial neighbors can be the same as            that used in HEVC merge mode.    -   9. When in the first stage of identifying a temporal vector does        not include information identifying a reference picture, the        motion source picture as shown in FIG. 9, may be simply set to        be a fixed picture, e.g., the co-located picture used for TMVP.        -   a. In such a case, the vector may only be identified from            the motion vectors that point to such a fixed picture.        -   b. In such a case, the vector may only be identified from            the motion vectors that point to any picture but further            scaled towards the fixed picture.    -   10. When in the first stage of identifying a vector consists        identifying a reference picture, the motion source picture as        shown in FIG. 9, one or more of the following additional checks        may apply for a candidate motion vector.        -   a. If the motion vector is associated with a picture or            slice that is Intra coded, such a motion vector is            considered as unavailable and cannot be used to be converted            to the vector.        -   b. If the motion vector identifies an Intra block (by e.g.,            adding the current center coordinate with the motion vector)            in the associated picture, such a motion vector is            considered as unavailable and cannot be used to be converted            to the vector.    -   11. When in the first stage of identifying a vector, the        components of the vector may be set to be (half width of the        current PU, half height of the current PU), so that it        identifies a bottom-right pixel position in the motion source        picture. Here (x, y) indicates a horizontal and vertical        components of one motion vector.        -   a. Alternatively, the components of the vector may be set to            be (sum(half width of the current PU, M), sum(half height of            the current PU, N)) where the function sum(a, b) returns the            sum of a and b. In one example, when the motion information            is stored in 4×4 unit, M and N are both set to be equal            to 2. In another example, when the motion information is            stored in 8×8 unit, M and N are both set to be equal to 4.    -   12. The sub-block/sub-PU size when ATMVP applies is signaled in        a parameter set, e.g., sequence parameter set of picture        parameter set. The size ranges from the least PU size to the CTU        size. The size can be also pre-defined or signaled. The size can        be, e.g., as small as 4×4. Alternatively, the sub-block/sub-PU        size can be derived based on the size of PU or CU. For example,        the sub-block/sub-PU can be set equal to max (4×4, (width of        CU)>>M). The value of M can be pre-defined or signaled in the        bitstream.    -   13. The maximum number of merge candidates may be increased by 1        due to the fact that ATMVP can be considered as a new merge        candidate. For example, compared to HEVC which takes up to 5        candidates in a merge candidate list after pruning, the maximum        number of merge candidates can be increased to 6.        -   a. Alternatively, pruning with conventional TMVP candidate            or unification with the conventional TMVP candidate can be            performed for ATMVP such that the maximum number of merge            candidates can be kept as unchanged.        -   b. Alternatively, when ATMVP is identified to be available,            a spatial neighboring candidate is excluded from the merge            candidate list, e.g., the last spatial neighboring candidate            in fetching order is excluded.    -   14. When multiple spatial neighboring motion vectors are        considered to derive the temporal vector, a motion vector        similarity may be calculated based on the neighboring motion        vectors of the current PU as well as the neighboring motion        vectors identified by a specific temporal vector being set equal        to a motion vector. The one that leads to the highest motion        similarity may be chosen as the final temporal vector.        -   a. In one alternative, for each motion vector from a            neighboring position N, the motion vector identifies a block            (same size as the current PU) in the motion source picture,            wherein its neighboring position N contains a set of the            motion information. This set of motion vector is compared            with the set of motion information as in the neighboring            position N of the current block.        -   b. In another alternative, for each motion vector from a            neighboring position N, it identifies a block in the motion            source picture, wherein its neighboring positions contain            multiple sets of motion information. These multiple sets of            motion vector are compared with the multiple sets of motion            information from the neighboring positions of the current PU            in the same relative positions. A motion information            similarity is calculated. For example, the current PU has            the following sets of motion information from A1, B1, A0 and            B0, denoted as MI_(A1), MI_(B1), MI_(A0) and MI_(B0). For a            temporal vector TV, it identifies a block corresponding to            the PU in the motion source picture. Such a block has motion            information from the same relative A1, B1, A0 and B0            positions, and denoted as TMI_(A1), TMI_(B1), TMI_(A0) and            TMI_(B0). The motion similarity as determined by TV is            calculated as MS_(tv)=Σ_(Nε{A1,B1,A0,B0}) MVSim(MI_(N),            TMI_(N)), wherein MVSim defines the similarity between two            sets of motion information.        -   c. In both of the above cases, the motion similarity MVSim            can be used, wherein the two input parameters are the two            motion information, each contains up to two motion vectors            and two reference indices. Since each pair of the motion            vectors in list X are actually associated with reference            pictures in different list X of different pictures, the            current picture and the motion source picture. For each of            the two motion vectors MVX_(N) and TMVX_(N) (with X being            equal to 0 or 1), the motion vector difference MVDX_(N) can            be calculated as MVX_(N)−TMVX_(N). Afterwards, the            difference MVSimX is calculated as e.g.,            abs(MVDX_(N)[0])+abs(MVDX_(N)[1]), or (MVDX_(N)[0]            *MVDX_(N)[0]+MVDX_(N)[1]*MVDX_(N)[1]). If both sets of            motion information contains available motion vectors, MVSim            is set equal to MVSim0+MVSim1.            -   i. In order to have a unified calculation of the motion                difference, both of the motion vectors need to be scaled                towards the same fixed picture, which can be, e.g., the                first reference picture RefPicListX[0] of the list X of                the current picture.            -   ii. If the availability of the motion vector in list X                from the first set and the availability of the motion                vector in list X from the second set are different,                i.e., one reference index is −1 while the other is not,                such two sets of motion information are considered as                not similar in direction X. If the two sets are not                similar in both sets, the final MVSim function may                return a big value T, which may be, e.g., considered as                infinite.            -   iii. Alternatively, for a pair of sets of motion                information, if one is predicted from list X (X being                equal to 0 or 1) but not list Y (Y being equal to 1−X)                and the other has the same status, a weighting between 1                and 2 (e.g., MVSim is equal to MVSimX*1.5) may be used.                When one set is only predicted from list X and the other                is only predicted from list Y, MVSim is set to the big                value T.            -   iv. Alternatively, for any set of motion information, as                long as one motion vector is available, both motion                vectors will be produced. In the case that only one                motion vector is available (corresponding to list X), it                is scaled to form the motion vector corresponding to the                other list Y.        -   d. Alternatively, the motion vector may be measured based on            differences between the neighboring pixels of the current PU            and the neighboring pixels of the block (same size as the            current PU) identified by the motion vector. The motion            vector that leads to the smallest difference may be chosen            as the final temporal vector.    -   15. When deriving the temporal vector of the current block,        motion vectors and/or temporal vectors from neighboring blocks        that are coded with ATMVP may have a higher priority than motion        vectors from other neighboring blocks.        -   a. In one example, only temporal vectors of neighboring            blocks are checked first, and the first available one can be            set to the temporal vector of the current block. Only when            such temporal vectors are not present, normal motion vectors            are further checked. In this case, temporal vectors for            ATMVP coded blocks need to be stored.        -   b. In another example, only motion vectors from ATMVP coded            neighboring blocks are checked first, and the first            available one can be set to the temporal vector of the            current block. Only when such temporal vectors are not            present, normal motion vectors are further checked.        -   c. In another example, only motion vectors from ATMVP coded            neighboring blocks are checked first, and the first            available one can be set to the temporal vector of the            current block. If such motion vectors are not available, the            checking of temporal vector continues similar as in bullet            15 a.        -   d. In another example, temporal vectors from neighboring            blocks are checked first, the first available one can be set            to the temporal vector of the current block. If such motion            vectors are not available, the checking of temporal vector            continues similar as in bullet 15 b.        -   e. In another example, temporal vectors and motion vectors            of ATMVP coded neighboring blocks are checked first, the            first available one can be set to the temporal vector of the            current block. Only when such temporal vectors and motion            vectors are not present, normal motion vectors are further            checked.    -   16. When multiple spatial neighboring motion vectors are        considered to derive the temporal vector, a motion vector may be        chosen so that it minimizes the distortion that is calculated        from the pixel domain, e.g., template matching may be used to        derive the temporal vector such that the one leads to minimal        matching cost is selected as the final temporal vector.    -   17. Derivation of a set of motion information from a        corresponding block (in the motion source picture) is done in a        way that when a motion vector is available in the corresponding        block for any list X (denote the motion vector to be MVX), for        the current sub-PU of the ATMVP candidate, the motion vector is        considered as available for list X (by scaling the MVX). If the        motion vector is unavailable in the corresponding block for any        list X, the motion vector is considered as unavailable for list        X.        -   a. Alternatively, when motion vector in the corresponding            block is unavailable for list X but available for list 1−X            (denoted 1−X by Y and denote the motion vector to be MVY),            the motion vector is still considered as available for list            X (by scaling the MVY towards the target reference picture            in list X).        -   b. Alternatively, or in addition, when both motion vectors            in the corresponding block for list X and list Y (equal to            1−X) are available, the motion vectors from list X and list            Y are not necessary used to directly scale and generate the            two motion vectors of a current sub-PU by scaling.            -   i. In one example, when formulating the ATMVP candidate,                the low-delay check as done in TMVP applies to each                sub-PU. If for every picture (denoted by refPic) in                every reference picture list of the current slice,                picture order count (POC) value of refPic is smaller                than POC of current slice, current slice is considered                with low-delay mode. In this low-delay mode, motion                vectors from list X and list Y are scaled to generate                the motion vectors of a current sub-PU for list X and                list Y, respectively. When not in the low-delay mode,                only one motion vector MVZ from MVX or MVY is chosen and                scaled to generate the two motion vectors for a current                sub-PU. Similar to TMVP, in such a case Z is set equal                to collocated_from_10_flag, meaning that it depends on                whether the co-located picture as in TMVP is in the list                X or list Y of the current picture. Alternatively, Z is                set as follows: if the motion source picture is                identified from list X, Z is set to X. Alternatively, in                addition, when the motion source pictures belong to both                reference picture lists, and RefPicList0[idx0] is the                motion source picture that is first present in list 0                and RefPicList(1)[idx1] is the motion source picture                that is first present in list 1, Z is set to be 0 if                idx0 is smaller than or equal to idx1, and set to be 1                otherwise.    -   18. The motion source picture may be signaled, e.g., generated        by video encoder 20 in a coded bitstream. In detail, a flag        indicating whether the motion source picture is from list 0 or        list 1 is signaled for a B slice. Alternatively, in addition, a        reference index to a list 0 or list 1 of the current picture may        be signaled to identify the motion source picture.

When identifying a temporal vector, a vector is considered asunavailable (thus other ones can be considered) if it points to an Intracoded block in the associated motion source picture.

FIG. 5 is a conceptual diagram illustrating sub-PU motion predictionfrom a reference picture. In this example, current picture 180 includesa current PU 184 (e.g., a PU). In this example, motion vector 192identifies PU 186 of reference picture 182 relative to PU 184. PU 186 ispartitioned into sub-PUs 188A-188D, each having respective motionvectors 190A-190D. Thus, although current PU 184 is not actuallypartitioned into separate sub-PUs, in this example, current PU 184 maybe predicted using motion information from sub-PUs 188A-188D. Inparticular, a video coder may code sub-PUs of current PU 184 usingrespective motion vectors 190A-190D. However, the video coder need notcode syntax elements indicating that current PU 184 is split intosub-PUs. In this manner, current PU 184 may be effectively predictedusing multiple motion vectors 190A-190D, inherited from respectivesub-PUs 188A-188D, without the signaling overhead of syntax elementsused to split current PU 184 into multiple sub-PUs.

FIG. 6 is a conceptual diagram illustrating relevant pictures in ATMVP(similar to TMVP). In particular, FIG. 9 illustrates current picture204, motion source picture 206, and reference pictures 200, 202. Moreparticularly, current picture 204 includes current block 208. Temporalmotion vector 212 identifies corresponding block 210 of motion sourcepicture 206 relative to current block 208. Corresponding block 210, inturn, includes motion vector 214, which refers to reference picture 202and acts as an advanced temporal motion vector predictor for at least aportion of current block 208, e.g., a sub-PU of current block 208. Thatis, motion vector 214 may be added as a candidate motion vectorpredictor for current block 208. If selected, at least a portion ofcurrent block 208 may be predicted using a corresponding motion vector,namely, motion vector 216, which refers to reference picture 200.

Sub-PU related techniques for HEVC are also described in U.S.Application Nos. 62/174,393 and 62/295,329, the entire content of bothof which is incorporated by reference herein. A flowchart showing anexample technique for spatial-temporal motion vector predictorderivation is shown below in FIG. 7.

To enhance the performance using sub-PU motion prediction,spatial-temporal motion information of neighboring sub-PU's (ATMVP_EXT)are exploited as described in U.S. Application Nos. 62/174,393 and62/295,329. In this example, the motion vector for each sub-PU isderived from the information of neighboring blocks in three-dimensionaldomain. It means the neighboring blocks could be the spatial neighborsin the current picture or the temporal neighbors in previous codedpictures. FIG. 7 shows the flow chart of the spatial-temporal motionvector predictor (STMVP) derivation process. Besides what are describedbelow, the methods described above for ATMVP (e.g., bullet #1, #2, #3,#4, #6, #7, #12, #13) could be directly extended to STMVP.

The method of FIG. 7 may be performed by video encoder 20 and/or videodecoder 30 (as described in more detail below). For generality, themethod of FIG. 7 is explained as being performed by a “video coder,”which again, may correspond to either of video encoder 20 or videodecoder 30.

Initially, a video coder obtains an available motion field from spatialor temporal neighboring blocks for a current sub-PU of a PU (230). Thevideo coder then derives motion information from the obtainedneighboring motion field (232). The video coder then determines whethermotion information for all sub-PUs of the PU has been derived (234). Ifnot (“NO” branch of 234), the video coder derives motion information fora remaining sub-PU (230). On the other hand, if motion information forall sub-PUs has been derived (“YES” branch of 234), the video coderdetermines availability of a spatial-temporal sub-PU motion predictor(236), e.g., as explained above. The video coder inserts thespatial-temporal sub-PU motion predictor into a merge list, if thespatial-temporal sub-PU motion predictor is available (238).

Although not shown in the method of FIG. 7, the video coder may thencode the PU (e.g., each of the sub-PUs of the PU) using the mergecandidate list. For instance, when performed by video encoder 20, videoencoder 20 may calculate residual block(s) for the PU (e.g., for eachsub-PU) using the sub-PUs as predictors, transform and quantize theresidual block(s), and entropy encode the resulting quantized transformcoefficients. Video decoder 30, similarly, may entropy decode receiveddata to reproduce quantized transform coefficients, inverse quantize andinverse transform these coefficients to reproduce the residual block(s),and then combine the residual block(s) with the corresponding sub-PUs todecode a block corresponding to the PU.

In the following description, the term “block” is used to refer theblock-unit for storage of prediction related info, e.g., inter or intraprediction, intra prediction mode, motion information etc. Suchprediction info is saved and may be used for coding future blocks, e.g.,predicting the prediction mode information for future blocks. In AVC andHEVC, the size of such a block is 4×4. It is noted that in the followingdescription, ‘PU’ is used to indicate the inter-coded block unit andsub-PU to indicate the unit that derives the motion information fromneighbouring blocks.

Any combination of the following techniques may be applied.

FIG. 8 is a conceptual diagram illustrating an example currentprediction unit (PU) 250 and neighboring sub-PUs 252A-252I. Currentblock 250 includes sub-PUs 254A-254P. When a PU includes multiplesub-PUs, the size of each of the sub-PUs is usually equal to or biggerthan that neighboring block size. In the example of FIG. 8, sub-PUs252A-252I represent neighboring blocks that are outside of current PU250, and sub-PUS 254A-254P represent the sub-PUs in current PU 250. Inthis example, the sizes of sub-PUs 254A-254P neighboring sub-PUs252A-252I are the same. For example, the size may be equal to 4×4.

By contrast, FIG. 9 is a conceptual diagram illustrating another examplecurrent PU 260 including sub-PUs 262A-262D that are larger thanneighboring blocks 264A-2641. In other examples, sub-PUs may havenon-square shapes, such as rectangles or triangles.

In some examples, the sizes of sub-PUs may be signalled in a sliceheader of a slice including blocks partitioned into the sub-PUs.

Alternatively, the process in bullet #12 of the discussion above relatedto ATMPV can be extended. Consider the case in FIG. 8, assume the rasterscan order (254A, 254B, 254C, 254D, 254E, and so on) is applied tosub-PUs 254A-254P for their motion prediction derivation in thefollowing description. However, other scan orders may be applied alsoand it should be noted that the techniques of this disclosure are notlimited to raster scan order only.

Here, neighboring blocks may be classified into two different types:spatial and temporal. A spatial neighboring block is an already codedblock or an already scanned sub-PU that is in the current picture orslice and neighboring to the current sub-PU, such as spatial neighboringsub-PUs 252A-252I of FIG. 8. A temporal neighboring block (not shown inFIG. 8) is a block in the previously coded picture and neighboring tothe co-located block of the current sub-PU. In one example, all thereference pictures associated with current PU are used to obtain thetemporal neighboring block. In another example, a sub-set of referencepictures are used for STMVP derivation, e.g., only the first entry ofeach reference picture list is used.

Following this definition, for sub-PU 254A, all neighboring blocks252A-252P and their collocated blocks in previous coded pictures arespatial and temporal neighboring blocks that are treated as available.According to raster scan order, blocks 254B-254P are not spatiallyavailable. Though, all sub-PUs (from 254A to 254P) are temporallyavailable neighboring blocks for sub-PU (A), because their motioninformation can be found in their collocated blocks in previous codedpictures. Take sub-PU 254G as another example, its spatial neighboringblocks that are available include those from 252A-252I and also from254A-254F. In some examples, certain restrictions may be applied to thespatial neighbouring blocks, e.g., the spatial neighbouring blocks(i.e., sub-PUs 252A-252I) may be restricted to be in the sameLCU/slice/tile as current block 250 in order to be considered“available.”

A subset of all available neighboring blocks may be selected to derivemotion information or motion field for each sub-PU. The subset used forderivation of each PU may be pre-defined, alternatively, it may besignalled as high level syntax in slice header/PPS/SPS. To optimize thecoding performance, the subset may be different for each sub-PU. Inpractice, a fixed pattern of location for the subset is preferred forsimplicity. For example, each sub-PU may use its immediate above spatialneighbor, its immediate left spatial neighbor and its immediatebottom-right temporal neighbor as the subset. As shown in FIG. 8, whenconsidering sub-PU 254J, the block above (sub-PU 254F) and the blockleft (sub-PU 254I) are spatially available neighboring blocks and thebottom-right block (sub-PU 254O) is a temporally available neighboringblock. With such a subset, sub-PUs 254A-254P in current PU 250 may beprocessed sequentially, due to processing dependency.

To allow paralleling processing of each of sub-PUs 254A-254P in currentPU 250, a different subset of neighboring sub-PUs 252A-252I may bedefined and used. In one example, a subset only contains spatialneighbor blocks that do not belong to current PU 250, e.g., neighboringsub-PUs 252A-252I. In this case, parallel processing would be possible.In another example, for a given one of sub-PUs 254A-254P, if its spatialneighboring block is within current PU 250, the collocated block of thatspatial neighboring block may be put in the subset and used to derivethe motion information of the current sub-PU. For example, whenconsidering sub-PU 254J, the temporal collocated blocks of the aboveblock (sub-PU 254F) and the left block (sub-PU 254I) and bottom-rightblock (sub-PU 254O) are selected as the subset to derive the motion ofthe sub-PU (sub-PU 254J). In this case, the subset for sub-PU 254Jcontains three temporal neighboring blocks. In another example,partially-parallel processing may be enabled wherein one PU is splitinto several regions and each region (covering several sub-PUs) could beprocessed independently.

Sometimes the neighboring blocks are intra coded, and it may bedesirable to have a rule to determine replacement motion information forthose blocks for better motion prediction and coding efficiency. Forexample, considering sub-PU 254A, there might be cases where sub-PUs252B, 252C, and 252F are intra-coded, and sub-PUs 252A, 252D, 252E,252G, 252H, and 252I are inter-coded.

For spatial neighbors, a pre-defined order may be used to populate themotion information of intra-coded blocks with that of the first foundinter coded block. For example, the searching order of the aboveneighbors can be set as starting from the immediate above neighborrightward until the rightmost neighbor, meaning the order of sub-PUs252B, 252C, 252D, and 252E. The search order of the left neighbors canbe set as starting from the immediate left neighbor downward until thebottommost neighbor, meaning the orders of sub-PUs 252F, 252G, 252H, and252I. If no inter-coded block is found through the search process, thenabove or left spatial neighbor is considered unavailable.

For temporal neighbors, the same rule as specified in the TMVPderivation can be used. However, it should be noted that other rules canalso be used, e.g., rules based on motion direction, temporal distance(search in different reference pictures) and spatial locations, etc.

For each neighboring block, motion vector scaling is applied to itsmotion vector based on each reference picture list in order to map allthe neighboring blocks' motion vectors to a same reference picture ineach list. There are two steps: first, determine a source motion vectorto be used for scaling. Second, determine a target reference picturewhere the source motion vector is projected to. For the first step,several methods can be used.

-   -   (a) for each reference list, motion vector scaling is        independent from motion vector in another reference list; For a        given block's motion information, if there is no motion vector        in a reference list (e.g., uni-prediction mode instead of        bi-prediction mode), no motion vector scaling is performed for        that list.    -   (b) motion vector scaling is not independent from motion vector        in another reference list; for a given block's motion        information, if no motion vector is unavailable in a reference        list, it can be scaled from the one in another reference list.    -   (c) both motion vectors are scaled from one pre-defined        reference list (as in TMVP mentioned above).

As one example, method (a) is used for scaling motion vectors of spatialneighboring blocks, and method (c) is used for scaling motion vectors oftemporal neighboring blocks.

As for the second step, the target reference picture can be selectedaccording to a certain rule based on the motion information (e.g.,reference pictures) of available spatial neighboring blocks. One exampleof such a rule is the majority rule, i.e., selecting the referencepicture shared by majority of the blocks. In this case there is nosignaling needed for the target reference picture from the encoder todecoder because the same information can also be inferred at decoderside using the same rule. Alternatively, such reference picture may alsobe specified explicitly in slice header, or signalled in some othermethods to decoder. The target reference picture is determined as thefirst reference picture (refidx=0) of each reference list.

After retrieving motion information from neighboring blocks asillustrated in the previous section and motion scaling process (ifneeded), the motion information of the current sub-PU is derived. Assumethere are N available neighboring blocks with motion information for onegiven sub-PU. First, the prediction direction (InterDir) has to bedetermined. The simplest method is as follows:

-   -   a. InterDir is initialized as zero, then looping through the        motion information of N available neighboring blocks;    -   b. InterDir=(InterDir bitwiseOR 1), if there is at least one        motion vector in List 0;    -   c. InterDir=(InterDir bitwiseOR 2), if there is at least one        motion vector in List 1.

Here “bitwiseOR” represent the bitwise OR operation. The value ofInterDir is defined as: 0 (no inter prediction), 1 (inter predictionbased on List 0), 2 (inter prediction based on List 1), and 3 (interprediction based on both List 0 and List 1).

Alternatively, similar to the determination on target reference picturefor motion vector scaling described above, the majority rule may be usedto determine the value of InterDir for the given sub-PU based on allavailable neighboring blocks' motion information.

After InterDir is determined, motion vectors can be derived. For eachreference list based on the derived InterDir, there may be M motionvectors (M<=N) available through motion vector scaling to a targetreference picture as described above. The motion vector for thereference list can be derived as:

(MV _(x) ,MV _(y))=((Σ_(i=0) ^(M) w _(i) *MV _(xi) +O _(i))/Σ_(i=0) ^(M)w _(i),(Σ_(j=0) ^(M) w _(j) *MV _(yj) +O _(j))/Σ_(j=0) ^(M) w _(j))

where w_(i) and w_(j) are the weighting factors for the horizontal andthe vertical motion component respectively, and O_(i) and O_(j) are theoffset values that are dependent on the weighting factors.

The weighting factors may be determined based on various factors. In oneexample, the same rule may be applied to all sub-PUs within one PU. Therule may be defined as follows:

For example, the weighting factor can be determined based on thelocation distance of the current sub-PU and a corresponding neighboringblock.

In another example, the weighting factor can also be determined based onthe POC distance between the target reference picture and the referencepicture associated with a corresponding neighboring block's motionvector before scaling.

In yet another example, the weighting factor may be determined based onmotion vector difference or consistency.

For simplicity, all the weighting factors may also be set to 1.

Alternatively, different rules may be applied to sub-PUs within one PU.For example, the above rule may be applied, in addition, for sub-PUslocated at the first row/first column, the weighting factors for motionvectors derived from temporal neighboring blocks are set to 0 while forthe remaining blocks, the weighting factors for motion vectors derivedfrom spatial neighboring blocks are set to 0.

It should be noted that in practice, the equations above may beimplemented as it is, or simplified for easy implementation. Forexample, to avoid division or floating point operation, fixed pointoperation may be used to approximate the equation above. One instance isthat to avoid divide by 3, one may instead choose to multiply with43/128 to replace division operation with multiplication and bit-shift.Those variations in implementation should be considered covered underthe same spirit of the techniques of this disclosure.

Alternatively, non-linear operation may be also applied to derive themotion vectors, such as median filter.

In some examples, even when the motion vector predictors of each sub-PUare available, the STMVP mode may be reset to be unavailable for one PU.

For example, once a motion vector predictor of each sub-PU is derivedfor a given PU, some availability checks are performed to determine ifSTMVP mode should be made available for the given PU. Such an operationis used to eliminate the cases where it is very unlikely for STMVP modeto be finally chosen for a given PU. When STMVP mode is not available,mode signaling does not include STMVP. In case that STMVP mode isimplemented by inserting SMTVP in merge list, the merge list doesn'tinclude this STMVP candidate when STMVP mode is determined to be notavailable. As a result, signaling overhead may be reduced.

Consider one PU partitioned into M sub-PUs. In one example, if N1(N1<=M) sub-PUs among the M sub-PUs have the same motion vectorpredictor (i.e., same motion vectors and same reference pictureindices), STMVP is only made available when N1 is smaller than athreshold or the predictor is different from other motion vectorpredictors (with smaller merge index) in the merge list. In anotherexample, if N2 (N2<=M) sub-PUs under STMVP mode share the same motionvector predictors as corresponding sub-PUs under ATMVP, STMVP is onlymade available when N2 is smaller than another threshold.

In one example of this disclosure, both thresholds for N1 and N2 are setequal to M.

In some examples, if STMVP is available, it is inserted into merge list.The process in bullet #1 above can be extended and STMVP can be insertedeither before or after ATMVP. In one example, STMVP is inserted rightafter ATMVP in the merge list.

When a syntax element is coded with context adaptive binary arithmeticcoding (CABAC), a context model is applied to represent conditionalprobability. In HEVC, a CABAC coder determines different context modelsfor different syntax elements. The CABAC coder can choose one contextmodel from several candidate context models for a syntax element in someexamples, based on the coding context, such as the bin number orinformation of decoded neighboring blocks. For example, three candidatecontext models named skip_flag_C[0], skip_flag_C[1] and skip_flag_C[2]can be used to code the syntax element cu_skip_flag which indicateswhether one CU is coded with skip mode or not.

To choose the appropriate context from the three candidate, the CABACcoder may calculate context index x as:

x=(cu_skip_flag[xNbL][yNbL]&& availableL)+(cu_skip_flag[xNbA][yNbA]&&availableA)

wherein the luma location (x0, y0) specifies the top-left luma sample ofthe current luma block relative to the top-left sample of the currentpicture; the location xNbL, yNbL) is set equal to (x0−1, y0) and thevariable availableL, specifying the availability of the block locateddirectly to the left of the current block, i.e., block L in FIG. 10; thelocation (xNbA, yNbA) is set equal to (x0, y0−1) and the variableavailableA specifying the availability of the coding block locateddirectly above the current block, i.e., block A in FIG. 10 andcu_skip_flag[xNbL][yNbL] and cu_skip_flag[xNbA][yNbA] represent thecu_skip_flag of the left block L and above block A in FIG. 10respectively. Neighboring blocks used to derive the context informationof cu_skip_flag is illustrated in FIG. 10.

As described above, there are many priority-based candidate lists. Eachcandidate is inserted into the candidate list according to a predefinedpriority. For example, in HEVC, Merge candidate list, AMVP candidatelist, intra most probable mode (MPM) list are constructed by insertingcandidates based on a predefined order (or according to a predefinedpriority). As shown in FIG. 11, the merge candidate list is constructedby inserting the spatial merging candidate by a predefined order(A1→B1→B0→A0→B2). Such a fixed order may not be able to capture localcharacteristics. If flexible order could be applied by putting acandidate with higher chance to be selected before other candidates,higher coding performance may be expected.

In techniques of this disclosure, geometry information may be usedbetween the current block and the neighboring blocks to determine thepriority or insertion order for the construction of candidate lists suchas merging candidate list, AMVP list and intra MPM list. Moreover, thisgeometry information can be used for the determination of the contextfor CABAC coding.

The following itemized methods may be applied individually.Alternatively, any combination of them may be applied.

(1) In one example, the distance between a representative point ofcurrent block and a representative point of the neighboring block whichthe candidate belongs to is used as the geometry information todetermine the priority or insertion order for the construction of thecandidate lists. The term “block” (e.g., Block0-Block4 and Current Blockin FIG. 12) used here can be a coding unit/block, prediction unit/block,sub-PU, transform unit/block or any other coding structure. Moreover,the unit block is the basic unit to store the coding information such asmotion information (motion vectors, reference picture index, interprediction directions and so on), intra prediction modes, transforminformation and so on. For example, the size of this unit block may be4×4. As shown in FIG. 12, the candidates A0, A1, B0, B1 and B2 arederived from the unit blocks covered by the neighboring blocks Block0,Block1, Block2, Block3 and Block4, respectively.

-   -   a. In one example, the shorter distance between that candidate's        representative point and current representative point has higher        priority or vice versa.    -   b. In one example, the distance can be LN-norm distance (N can        be 1, 2 or any other positive integer).

(2) In item 1, the representative point of current block can be anypoint within current block. In one example, as shown in FIG. 12, therepresentative point of current block is the center point of currentblock. FIG. 12 illustrates an example of geometric information ofspatial merging candidates.

(3) In item 1, the representative point of the neighboring block can beany point within the neighboring block. In one example, as shown in FIG.12, the representative point of a neighboring block is the center pointof the neighboring block.

(4) Alternatively, as shown in FIG. 13, the representative point of aneighboring block is the center point of the sub-PU covered by theneighboring block. For example, if neighbor blocks are coded as sub-PUmodes such as FRUC, Affine, ATMVP, the center point of that sub-PU isused as the representative point for that block. FIG. 13 illustrates anexample of geometric information of spatial merging candidates. As shownin FIG. 13, since Block 1 is coded as sub-PU mode, the representativepoint of the sub-PU which candidate A1 belongs to is used to derive thegeometric priority.

(5) Additionally or alternatively, the representative point can be anypoint within current block or the neighboring block determinedadaptively according to coding information such as MV, reference pictureinformation, intra modes, transform coefficients, residual information,and so on.

-   -   a. In one example, for constructing the intra mode candidate        list, the center point may be replaced by the top-left point        within a block.

(6) The above mentioned methods can be applied to determine the priorityto construct the candidate list, individually or in any combination ofthe other priorities.

-   -   a. In one example, when two or more candidates have the same        geometry priority (e.g., same distance between representative        points), a predefined priority can be used to distinguish them.        For example, an insertion order (A1→B1→B0→A0→B2) can be used.    -   b. Alternatively, the other priority can be the coding        information such as inter prediction direction (e.g., L0, L1 or        bi), the MVs, the intra prediction modes, the POC of the        reference pictures and so on.

(7) The above mentioned methods may be applied to certain blocks.

-   -   a. In one example, the above method is applied to blocks with        different width and height.    -   b. Alternatively, the above method is applied to blocks with the        ratio of width and height larger than K or smaller than 1/K        wherein K is a positive integer value and larger than 1.    -   c. Alternatively, the above method is applied to blocks with        certain sizes.

(8) The above mentioned methods may be partially applied to some of thecandidates.

-   -   a. In one example, the geometry information is only used to        determine the order of spatial merging/intra mode candidates,        i.e., candidates derived from spatial neighboring blocks.    -   b. In one example, the geometry information is only used to        determine the order of the paired candidates (A1, B1).    -   c. In one example, the geometry information is only used to        determine the order of the paired candidates (A0, B0).

(9) Whether to use the geometry-based priority may be signaled in thebitstream.

-   -   a. In one example, for each coding unit/prediction        unit/transform unit, a flag may be signaled to indicate whether        the geometry-based priority or the predefined priority list        should be used.

(10) When the order of merge candidate list is modified according to thegeometry-based priority, the first candidate after re-ordering is usedin the first stage for ATMVP and/or STMVP processes.

-   -   a. Alternatively, the first candidate derived from the        predefined order is used in the first stage for ATMVP and/or        STMVP processes.

(11) The geometry information may be used for the determination ofcontexts for CABAC coding when information from neighboring blocks areutilized.

-   -   a. In one example, in addition to the left (such as L depicted        in FIG. 10) and the above block (such as A depicted in FIG. 10),        more neighboring blocks such as A0, A1, B0, B1 and B2 (same as A        in FIG. 10) as depicted in FIG. 11 are used to derive the        context of cu_skip_flag of the current block.    -   b. When multiple neighboring blocks (denote the total number        by M) are utilized for context modeling, only the information        from the first N blocks based on the geometry priority is        considered. Here, N is smaller than M. In one example, N is set        to 2 and M is set to 5.    -   c. Alternatively, furthermore, context modeling of other syntax        elements, which include but not limited to        cu_transquant_bypass_flag, cu_skip_flag, cbf, pred_mode_flag,        rqt_root_cbf, merge_idx, merge_flag, cbf_luma, cbf_cb, cbf_cr        may also use the above method.    -   d. In one example, the above method may be applied to certain        blocks, e.g., the width and height of a block is different, or        the ratio of width and height is larger than a threshold or        applied to blocks with certain sizes.    -   e. In one example, the CABAC context is determined by the coding        information of the neighboring blocks scaled by their associated        weighting factors. The associated weighting factors is derived        with the geometry information. For example, when selecting the        context for coding skip flag, x may be derived by the following        equation.

x=WL*(cu_skip_flag[xNbL][yNbL]&&availableL)+WA(cu_skip_flag[xNbA][yNbA]&& availableA)

The WL and WA are the associated weighting factor for left and aboveneighboring blocks, respectively. WL and WA can be derived according totheir geometry information. In one example, when the distance betweenthe representative point of neighbor block and current block is largerthan a predefined threshold, the associated weighting factor is set to avalue M; otherwise (when the distance is less than or equal to apredefined threshold), the associated weighting factor is set to a valueN.

-   -   f. In item 11.e, the neighboring blocks are not limited to left        and above blocks used in HEVC. The neighboring blocks can be any        one of the previously coded blocks.    -   g. In item 11.e, more values can be assigned for weighting        factors by introducing more thresholds.

(12) In another example, the geometry information of the neighboringblocks may be used to determine the priority or insertion order for theconstruction of candidate lists such as merging candidate list, AMVPlist and intra MPM list. Moreover, this geometry information can be usedfor the determination of the context for CABAC coding.

(13) In one example, the area of the neighboring block which thecandidate belongs to is used as a geometry information to determine thepriority or insertion order for the construction of the candidate lists.The term “block” used here can be coding unit/block, predictionunit/block, sub-PU, transform unit/block or any other coding structures.The block with smaller area has higher priority or vice versa.

(14) The area-based geometry information can be applied as the same asthe aforementioned methods as described in items 6 to 11.

FIG. 14 is a block diagram illustrating an example video encoding anddecoding system 10 that may be configured to perform the techniques ofthis disclosure for motion vector prediction. As shown in FIG. 14,system 10 includes a source device 12 that provides encoded video datato be decoded at a later time by a destination device 14. In particular,source device 12 provides the video data to destination device 14 via acomputer-readable medium 16. Source device 12 and destination device 14may comprise any of a wide range of devices, including desktopcomputers, notebook (i.e., laptop) computers, tablet computers, set-topboxes, telephone handsets such as so-called “smart” phones, so-called“smart” pads, televisions, cameras, display devices, digital mediaplayers, video gaming consoles, video streaming device, or the like. Insome cases, source device 12 and destination device 14 may be equippedfor wireless communication.

Destination device 14 may receive the encoded video data to be decodedvia computer-readable medium 16. Computer-readable medium 16 maycomprise any type of medium or device capable of moving the encodedvideo data from source device 12 to destination device 14. In oneexample, computer-readable medium 16 may comprise a communication mediumto enable source device 12 to transmit encoded video data directly todestination device 14 in real-time. The encoded video data may bemodulated according to a communication standard, such as a wirelesscommunication protocol, and transmitted to destination device 14. Thecommunication medium may comprise any wireless or wired communicationmedium, such as a radio frequency (RF) spectrum or one or more physicaltransmission lines. The communication medium may form part of apacket-based network, such as a local area network, a wide-area network,or a global network such as the Internet. The communication medium mayinclude routers, switches, base stations, or any other equipment thatmay be useful to facilitate communication from source device 12 todestination device 14.

In some examples, encoded data may be output from output interface 22 toa storage device. Similarly, encoded data may be accessed from thestorage device by input interface. The storage device may include any ofa variety of distributed or locally accessed data storage media such asa hard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile ornon-volatile memory, or any other suitable digital storage media forstoring encoded video data. In a further example, the storage device maycorrespond to a file server or another intermediate storage device thatmay store the encoded video generated by source device 12. Destinationdevice 14 may access stored video data from the storage device viastreaming or download. The file server may be any type of server capableof storing encoded video data and transmitting that encoded video datato the destination device 14. Example file servers include a web server(e.g., for a website), an FTP server, network attached storage (NAS)devices, or a local disk drive. Destination device 14 may access theencoded video data through any standard data connection, including anInternet connection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., DSL, cable modem, etc.), or acombination of both that is suitable for accessing encoded video datastored on a file server. The transmission of encoded video data from thestorage device may be a streaming transmission, a download transmission,or a combination thereof.

The techniques of this disclosure are not necessarily limited towireless applications or settings. The techniques may be applied tovideo coding in support of any of a variety of multimedia applications,such as over-the-air television broadcasts, cable televisiontransmissions, satellite television transmissions, Internet streamingvideo transmissions, such as dynamic adaptive streaming over HTTP(DASH), digital video that is encoded onto a data storage medium,decoding of digital video stored on a data storage medium, or otherapplications. In some examples, system 10 may be configured to supportone-way or two-way video transmission to support applications such asvideo streaming, video playback, video broadcasting, and/or videotelephony.

In the example of FIG. 14, source device 12 includes video source 18,video encoder 20, and output interface 22. Destination device 14includes input interface 28, video decoder 30, and display device 32. Inaccordance with this disclosure, video encoder 20 of source device 12and video decoder 30 of destination device 14 may be configured to applythe candidate list construction techniques of this disclosure for motionvector prediction. In other examples, a source device and a destinationdevice may include other components or arrangements. For example, sourcedevice 12 may receive video data from an external video source 18, suchas an external camera. Likewise, destination device 14 may interfacewith an external display device, rather than including an integrateddisplay device.

The illustrated system 10 of FIG. 14 is merely one example. Thetechniques of this disclosure for motion vector prediction may beperformed by any digital video encoding and/or decoding device. Althoughgenerally the techniques of this disclosure are performed by a videoencoding device, the techniques may also be performed by a videoencoder/decoder, typically referred to as a “CODEC.” Moreover, thetechniques of this disclosure may also be performed by a videopreprocessor. Source device 12 and destination device 14 are merelyexamples of such coding devices in which source device 12 generatescoded video data for transmission to destination device 14. In someexamples, devices 12, 14 may operate in a substantially symmetricalmanner such that each of devices 12, 14 include video encoding anddecoding components. Hence, system 10 may support one-way or two-wayvideo transmission between video devices 12, 14, e.g., for videostreaming, video playback, video broadcasting, or video telephony.

Video source 18 of source device 12 may include a video capture device,such as a video camera, a video archive containing previously capturedvideo, and/or a video feed interface to receive video from a videocontent provider. As a further alternative, video source 18 may generatecomputer graphics-based data as the source video, or a combination oflive video, archived video, and computer-generated video. In some cases,if video source 18 is a video camera, source device 12 and destinationdevice 14 may form so-called camera phones or video phones. As mentionedabove, however, the techniques described in this disclosure may beapplicable to video coding in general, and may be applied to wirelessand/or wired applications. In each case, the captured, pre-captured, orcomputer-generated video may be encoded by video encoder 20. The encodedvideo information may then be output by output interface 22 onto acomputer-readable medium 16.

Computer-readable medium 16 may include transient media, such as awireless broadcast or wired network transmission, or storage media (thatis, non-transitory storage media), such as a hard disk, flash drive,compact disc, digital video disc, Blu-ray disc, or othercomputer-readable media. In some examples, a network server (not shown)may receive encoded video data from source device 12 and provide theencoded video data to destination device 14, e.g., via networktransmission. Similarly, a computing device of a medium productionfacility, such as a disc stamping facility, may receive encoded videodata from source device 12 and produce a disc containing the encodedvideo data. Therefore, computer-readable medium 16 may be understood toinclude one or more computer-readable media of various forms, in variousexamples.

Input interface 28 of destination device 14 receives information fromcomputer-readable medium 16. The information of computer-readable medium16 may include syntax information defined by video encoder 20, which isalso used by video decoder 30, that includes syntax elements thatdescribe characteristics and/or processing of blocks and other codedunits, e.g., GOPs. Display device 32 displays the decoded video data toa user, and may comprise any of a variety of display devices such as acathode ray tube (CRT), a liquid crystal display (LCD), a plasmadisplay, an organic light emitting diode (OLED) display, or another typeof display device.

Video encoder 20 and video decoder 30 may operate according to a videocoding standard, such as the High Efficiency Video Coding (HEVC)standard, extensions to the HEVC standard, or subsequent standards, suchas ITU-T H.266. Alternatively, video encoder 20 and video decoder 30 mayoperate according to other proprietary or industry standards, such asthe ITU-T H.264 standard, alternatively referred to as MPEG-4, Part 10,Advanced Video Coding (AVC), or extensions of such standards. Thetechniques of this disclosure, however, are not limited to anyparticular coding standard. Other examples of video coding standardsinclude MPEG-2 and ITU-T H.263. Although not shown in FIG. 14, in someaspects, video encoder 20 and video decoder 30 may each be integratedwith an audio encoder and decoder, and may include appropriate MUX-DEMUXunits, or other hardware and software, to handle encoding of both audioand video in a common data stream or separate data streams. Ifapplicable, MUX-DEMUX units may conform to the ITU H.223 multiplexerprotocol, or other protocols such as the user datagram protocol (UDP).

Video encoder 20 and video decoder 30 each may be implemented as any ofa variety of suitable encoder circuitry, such as one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs),discrete logic, software, hardware, firmware or any combinationsthereof. When the techniques are implemented partially in software, adevice may store instructions for the software in a suitable,non-transitory computer-readable medium and execute the instructions inhardware using one or more processors to perform the techniques of thisdisclosure. Each of video encoder 20 and video decoder 30 may beincluded in one or more encoders or decoders, either of which may beintegrated as part of a combined encoder/decoder (CODEC) in a respectivedevice.

Video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-TH.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual andITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its ScalableVideo Coding (SVC) and Multiview Video Coding (MVC) extensions. Onejoint draft of MVC is described in “Advanced video coding for genericaudiovisual services,” ITU-T Recommendation H.264, March, 2010.

In addition, there is a newly developed video coding standard, namelyHigh Efficiency Video Coding (HEVC), developed by the JointCollaboration Team on Video Coding (JCT-VC) of ITU-T Video CodingExperts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG). Arecent draft of HEVC is availablefromphenix.int-evry.fr/jct/doc_end_user/documents/12_Geneva/wg11/JCTVC-L1003-v34.zip.The HEVC standard is also presented jointly in Recommendation ITU-TH.265 and International Standard ISO/IEC 23008-2, both entitled “Highefficiency video coding,” and both published October, 2014.

The JCT-VC developed the HEVC standard. The HEVC standardization effortsare based on an evolving model of a video coding device referred to asthe HEVC Test Model (HM). The HM presumes several additionalcapabilities of video coding devices relative to existing devicesaccording to, e.g., ITU-T H.264/AVC. For example, whereas H.264 providesnine intra-prediction encoding modes, the HEVC HM may provide as many asthirty-three intra-prediction encoding modes.

In general, the working model of the HM describes that a video frame orpicture may be divided into a sequence of treeblocks or largest codingunits (LCU) that include both luma and chroma samples. Syntax datawithin a bitstream may define a size for the LCU, which is a largestcoding unit in terms of the number of pixels. A slice includes a numberof consecutive treeblocks in coding order. A video frame or picture maybe partitioned into one or more slices. Each treeblock may be split intocoding units (CUs) according to a quadtree. In general, a quadtree datastructure includes one node per CU, with a root node corresponding tothe treeblock. If a CU is split into four sub-CUs, the nodecorresponding to the CU includes four leaf nodes, each of whichcorresponds to one of the sub-CUs.

Each node of the quadtree data structure may provide syntax data for thecorresponding CU. For example, a node in the quadtree may include asplit flag, indicating whether the CU corresponding to the node is splitinto sub-CUs. Syntax elements for a CU may be defined recursively, andmay depend on whether the CU is split into sub-CUs. If a CU is not splitfurther, it is referred as a leaf-CU. In this disclosure, four sub-CUsof a leaf-CU will also be referred to as leaf-CUs even if there is noexplicit splitting of the original leaf-CU. For example, if a CU at16×16 size is not split further, the four 8×8 sub-CUs will also bereferred to as leaf-CUs although the 16×16 CU was never split.

A CU has a similar purpose as a macroblock of the H.264 standard, exceptthat a CU does not have a size distinction. For example, a treeblock maybe split into four child nodes (also referred to as sub-CUs), and eachchild node may in turn be a parent node and be split into another fourchild nodes. A final, unsplit child node, referred to as a leaf node ofthe quadtree, comprises a coding node, also referred to as a leaf-CU.Syntax data associated with a coded bitstream may define a maximumnumber of times a treeblock may be split, referred to as a maximum CUdepth, and may also define a minimum size of the coding nodes.Accordingly, a bitstream may also define a smallest coding unit (SCU).This disclosure uses the term “block” to refer to any of a CU, PU, orTU, in the context of HEVC, or similar data structures in the context ofother standards (e.g., macroblocks and sub-blocks thereof in H.264/AVC).

A CU includes a coding node and prediction units (PUs) and transformunits (TUs) associated with the coding node. A size of the CUcorresponds to a size of the coding node and must be square in shape.The size of the CU may range from 8×8 pixels up to the size of thetreeblock with a maximum of 64×64 pixels or greater. Each CU may containone or more PUs and one or more TUs. Syntax data associated with a CUmay describe, for example, partitioning of the CU into one or more PUs.Partitioning modes may differ between whether the CU is skip or directmode encoded, intra-prediction mode encoded, or inter-prediction modeencoded. PUs may be partitioned to be non-square in shape. Syntax dataassociated with a CU may also describe, for example, partitioning of theCU into one or more TUs according to a quadtree. A TU can be square ornon-square (e.g., rectangular) in shape.

The HEVC standard allows for transformations according to TUs, which maybe different for different CUs. The TUs are typically sized based on thesize of PUs within a given CU defined for a partitioned LCU, althoughthis may not always be the case. The TUs are typically the same size orsmaller than the PUs. In some examples, residual samples correspondingto a CU may be subdivided into smaller units using a quadtree structureknown as “residual quad tree” (RQT). The leaf nodes of the RQT may bereferred to as transform units (TUs). Pixel difference values associatedwith the TUs may be transformed to produce transform coefficients, whichmay be quantized.

A leaf-CU may include one or more prediction units (PUs). In general, aPU represents a spatial area corresponding to all or a portion of thecorresponding CU, and may include data for retrieving a reference samplefor the PU. Moreover, a PU includes data related to prediction. Forexample, when the PU is intra-mode encoded, data for the PU may beincluded in a residual quadtree (RQT), which may include data describingan intra-prediction mode for a TU corresponding to the PU. As anotherexample, when the PU is inter-mode encoded, the PU may include datadefining one or more motion vectors for the PU. The data defining themotion vector for a PU may describe, for example, a horizontal componentof the motion vector, a vertical component of the motion vector, aresolution for the motion vector (e.g., one-quarter pixel precision orone-eighth pixel precision), a reference picture to which the motionvector points, and/or a reference picture list (e.g., List 0, List 1, orList C) for the motion vector.

Geometry information between a current block and neighboring blocks maydetermine priority or insertion order for the construction of thereference picture list (e.g., List 0, List 1, or List C) for the motionvector. Geometry information may include the distance between arepresentative point of the current block (e.g., a central point) and arepresentative point of the neighboring block which the candidatebelongs to. A higher priority may be indicated for neighboring blockswith a shorter distance between the representative point and therepresentative point of the current block. The representative point maybe the any point (e.g., a central point) within the block.

A leaf-CU having one or more PUs may also include one or more transformunits (TUs). The transform units may be specified using an RQT (alsoreferred to as a TU quadtree structure), as discussed above. Forexample, a split flag may indicate whether a leaf-CU is split into fourtransform units. Then, each transform unit may be split further intofurther sub-TUs. When a TU is not split further, it may be referred toas a leaf-TU. Generally, for intra coding, all the leaf-TUs belonging toa leaf-CU share the same intra prediction mode. That is, the sameintra-prediction mode is generally applied to calculate predicted valuesfor all TUs of a leaf-CU. For intra coding, a video encoder maycalculate a residual value for each leaf-TU using the intra predictionmode, as a difference between the portion of the CU corresponding to theTU and the original block. A TU is not necessarily limited to the sizeof a PU. Thus, TUs may be larger or smaller than a PU. For intra coding,a PU may be collocated with a corresponding leaf-TU for the same CU. Insome examples, the maximum size of a leaf-TU may correspond to the sizeof the corresponding leaf-CU.

Moreover, TUs of leaf-CUs may also be associated with respectivequadtree data structures, referred to as residual quadtrees (RQTs). Thatis, a leaf-CU may include a quadtree indicating how the leaf-CU ispartitioned into TUs. The root node of a TU quadtree generallycorresponds to a leaf-CU, while the root node of a CU quadtree generallycorresponds to a treeblock (or LCU). TUs of the RQT that are not splitare referred to as leaf-TUs. In general, this disclosure uses the termsCU and TU to refer to leaf-CU and leaf-TU, respectively, unless notedotherwise.

A video sequence typically includes a series of video frames orpictures. A group of pictures (GOP) generally comprises a series of oneor more of the video pictures. A GOP may include syntax data in a headerof the GOP, a header of one or more of the pictures, or elsewhere, thatdescribes a number of pictures included in the GOP. Each slice of apicture may include slice syntax data that describes an encoding modefor the respective slice. Video encoder 20 typically operates on videoblocks within individual video slices in order to encode the video data.A video block may correspond to a coding node within a CU. The videoblocks may have fixed or varying sizes, and may differ in size accordingto a specified coding standard.

As an example, the HM supports prediction in various PU sizes. Assumingthat the size of a particular CU is 2N×2N, the HM supportsintra-prediction in PU sizes of 2N×2N or N×N, and inter-prediction insymmetric PU sizes of 2N×2N, 2N×N, N×2N, or N×N. The HM also supportsasymmetric partitioning for inter-prediction in PU sizes of 2N×nU,2N×nD, nL×2N, and nR×2N. In asymmetric partitioning, one direction of aCU is not partitioned, while the other direction is partitioned into 25%and 75%. The portion of the CU corresponding to the 25% partition isindicated by an “n” followed by an indication of “Up”, “Down,” “Left,”or “Right.” Thus, for example, “2N×nU” refers to a 2N×2N CU that ispartitioned horizontally with a 2N×0.5N PU on top and a 2N×1.5N PU onbottom.

In general, intra-prediction involves predicting a block usingneighboring, previously coded pixels to the block (within the samepicture). Various intra-prediction modes, such as horizontal, vertical,and various diagonal modes, as well as DC and planar modes, may be used.Furthermore, certain modes may be considered “most probable,” based onintra-prediction modes used to intra-predict neighboring blocks. Inaccordance with the techniques of this disclosure, video encoder 20 andvideo decoder 30 may construct a most probable mode (MPM) list includingneighboring blocks to the current block as candidates, such thatcandidates within the MPM list are ordered, e.g., according to geometryinformation for the current block and the neighboring blocks, asdiscussed above.

In this disclosure, “N×N” and “N by N” may be used interchangeably torefer to the pixel dimensions of a video block in terms of vertical andhorizontal dimensions, e.g., 16×16 pixels or 16 by 16 pixels. Ingeneral, a 16×16 block will have 16 pixels in a vertical direction(y=16) and 16 pixels in a horizontal direction (x=16). Likewise, an N×Nblock generally has N pixels in a vertical direction and N pixels in ahorizontal direction, where N represents a nonnegative integer value.The pixels in a block may be arranged in rows and columns. Moreover,blocks need not necessarily have the same number of pixels in thehorizontal direction as in the vertical direction. For example, blocksmay comprise N×M pixels, where M is not necessarily equal to N.

Following intra-predictive or inter-predictive coding using the PUs of aCU, video encoder 20 may calculate residual data for the TUs of the CU.The PUs may comprise syntax data describing a method or mode ofgenerating predictive pixel data in the spatial domain (also referred toas the pixel domain) and the TUs may comprise coefficients in thetransform domain following application of a transform, e.g., a discretecosine transform (DCT), an integer transform, a wavelet transform, or aconceptually similar transform to residual video data. The residual datamay correspond to pixel differences between pixels of the unencodedpicture and prediction values corresponding to the PUs. Video encoder 20may form the TUs including the residual data for the CU, and thentransform the TUs to produce transform coefficients for the CU.

Following any transforms to produce transform coefficients, videoencoder 20 may perform quantization of the transform coefficients.Quantization generally refers to a process in which transformcoefficients are quantized to possibly reduce the amount of data used torepresent the coefficients, providing further compression. Thequantization process may reduce the bit depth associated with some orall of the coefficients. For example, an n-bit value may be rounded downto an m-bit value during quantization, where n is greater than m.

Following quantization, the video encoder may scan the transformcoefficients, producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) coefficients at the front of the array and to place lowerenergy (and therefore higher frequency) coefficients at the back of thearray. In some examples, video encoder 20 may utilize a predefined scanorder to scan the quantized transform coefficients to produce aserialized vector that can be entropy encoded. In other examples, videoencoder 20 may perform an adaptive scan. After scanning the quantizedtransform coefficients to form a one-dimensional vector, video encoder20 may entropy encode the one-dimensional vector, e.g., according tocontext-adaptive variable length coding (CAVLC), context-adaptive binaryarithmetic coding (CABAC), syntax-based context-adaptive binaryarithmetic coding (SBAC), Probability Interval Partitioning Entropy(PIPE) coding or another entropy encoding methodology. Video encoder 20may also entropy encode syntax elements associated with the encodedvideo data for use by video decoder 30 in decoding the video data.

To perform CABAC, video encoder 20 may assign a context within a contextmodel to a symbol to be transmitted. The context may relate to, forexample, whether neighboring values of the symbol are non-zero or not.To perform CAVLC, video encoder 20 may select a variable length code fora symbol to be transmitted. Codewords in VLC may be constructed suchthat relatively shorter codes correspond to more probable symbols, whilelonger codes correspond to less probable symbols. In this way, the useof VLC may achieve a bit savings over, for example, using equal-lengthcodewords for each symbol to be transmitted. The probabilitydetermination may be based on a context assigned to the symbol.

FIG. 15 is a block diagram illustrating an example of video encoder 20that may be configured to perform the techniques of this disclosure forgeometry-based priority lists. Video encoder 20 may perform intra- andinter-coding of video blocks within video slices. Intra-coding relies onspatial prediction to reduce or remove spatial redundancy in videowithin a given video frame or picture. Inter-coding relies on temporalprediction to reduce or remove temporal redundancy in video withinadjacent frames or pictures of a video sequence. Intra-mode (I mode) mayrefer to any of several spatial based coding modes. Inter-modes, such asuni-directional prediction (P mode) or bi-prediction (B mode), may referto any of several temporal-based coding modes.

As shown in FIG. 15, video encoder 20 receives a current video blockwithin a video frame to be encoded. In the example of FIG. 15, videoencoder 20 includes mode select unit 40, reference picture memory 64,summer 50, transform processing unit 52, quantization unit 54, andentropy encoding unit 56. Mode select unit 40, in turn, includes motioncompensation unit 44, motion estimation unit 42, intra-prediction unit46, and partition unit 48. For video block reconstruction, video encoder20 also includes inverse quantization unit 58, inverse transform unit60, and summer 62. A deblocking filter (not shown in FIG. 15) may alsobe included to filter block boundaries to remove blockiness artifactsfrom reconstructed video. If desired, the deblocking filter wouldtypically filter the output of summer 62. Additional filters (in loop orpost loop) may also be used in addition to the deblocking filter. Suchfilters are not shown for brevity, but if desired, may filter the outputof summer 50 (as an in-loop filter).

During the encoding process, video encoder 20 receives a video frame orslice to be coded. The frame or slice may be divided into multiple videoblocks. Motion estimation unit 42 and motion compensation unit 44perform inter-predictive coding of the received video block relative toone or more blocks in one or more reference frames to provide temporalprediction. Intra-prediction unit 46 may alternatively performintra-predictive coding of the received video block relative to one ormore neighboring blocks in the same frame or slice as the block to becoded to provide spatial prediction. Video encoder 20 may performmultiple coding passes, e.g., to select an appropriate coding mode foreach block of video data.

Moreover, partition unit 48 may partition blocks of video data intosub-blocks, based on evaluation of previous partitioning schemes inprevious coding passes. For example, partition unit 48 may initiallypartition a frame or slice into LCUs, and partition each of the LCUsinto sub-CUs based on rate-distortion analysis (e.g., rate-distortionoptimization). Mode select unit 40 may further produce a quadtree datastructure indicative of partitioning of an LCU into sub-CUs. Leaf-nodeCUs of the quadtree may include one or more PUs and one or more TUs.

Mode select unit 40 may select one of the coding modes, intra or inter,e.g., based on error results, and provides the resulting intra- orinter-coded block to summer 50 to generate residual block data and tosummer 62 to reconstruct the encoded block for use as a reference frame.Mode select unit 40 also provides syntax elements, such as motionvectors, intra-mode indicators, partition information, and other suchsyntax information, to entropy encoding unit 56.

Motion estimation unit 42 and motion compensation unit 44 may be highlyintegrated, but are illustrated separately for conceptual purposes.Motion estimation, performed by motion estimation unit 42, is theprocess of generating motion vectors, which estimate motion for videoblocks. A motion vector, for example, may indicate the displacement of aPU of a video block within a current video frame or picture relative toa predictive block within a reference frame (or other coded unit)relative to the current block being coded within the current frame (orother coded unit). A predictive block is a block that is found toclosely match the block to be coded, in terms of pixel difference, whichmay be determined by sum of absolute difference (SAD), sum of squaredifference (SSD), or other difference metrics. In some examples, videoencoder 20 may calculate values for sub-integer pixel positions ofreference pictures stored in reference picture memory 64. For example,video encoder 20 may interpolate values of one-quarter pixel positions,one-eighth pixel positions, or other fractional pixel positions of thereference picture. Therefore, motion estimation unit 42 may perform amotion search relative to the full pixel positions and fractional pixelpositions and output a motion vector with fractional pixel precision.

Motion estimation unit 42 calculates a motion vector for a PU of a videoblock in an inter-coded slice by comparing the position of the PU to theposition of a predictive block of a reference picture. The referencepicture may be selected from a first reference picture list (List 0) ora second reference picture list (List 1), each of which identify one ormore reference pictures stored in reference picture memory 64. Motionestimation unit 42 sends the calculated motion vector to entropyencoding unit 56 and motion compensation unit 44.

Motion compensation, performed by motion compensation unit 44, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation unit 42. Again, motion estimationunit 42 and motion compensation unit 44 may be functionally integrated,in some examples. Upon receiving the motion vector for the PU of thecurrent video block, motion compensation unit 44 may locate thepredictive block to which the motion vector points in one of thereference picture lists. Summer 50 forms a residual video block bysubtracting pixel values of the predictive block from the pixel valuesof the current video block being coded, forming pixel difference values,as discussed below. In general, motion estimation unit 42 performsmotion estimation relative to luma components, and motion compensationunit 44 uses motion vectors calculated based on the luma components forboth chroma components and luma components. Mode select unit 40 may alsogenerate syntax elements associated with the video blocks and the videoslice for use by video decoder 30 in decoding the video blocks of thevideo slice.

Furthermore, entropy encoding unit 56, or motion compensation unit 44,may apply the techniques of this disclosure when performing motionvector prediction, e.g., using merge mode or AMVP mode. In particular,when constructing a candidate list (e.g., a merge candidate list or anAMVP candidate list) used to predict a motion vector for a currentblock, entropy encoding unit 56 or motion compensation unit 44 mayarrange candidates within the candidate list according to priorityvalues for the candidates, where the priority values may representgeometry information for the candidates, as discussed in thisdisclosure. The geometry information may be, for example, distancesbetween representative points of a current block and neighboring blocksto the current block (which may include spatial and/or temporalneighboring blocks). As discussed above, the representative points maybe center points of the blocks, upper-left points of the blocks, or thelike. Entropy encoding unit 56 or motion compensation unit 44 may useany of the various techniques of this disclosure, alone or in anycombination, when calculating the priority values.

Video encoder 20 may be configured to perform any of the varioustechniques of this disclosure discussed above with respect to FIG. 14,and as will be described in more detail below. For example, motioncompensation unit 44 may be configured to code motion information for ablock of video data using AMVP or merge mode in accordance with thetechniques of this disclosure. Additionally or alternatively, intraprediction unit 46 may be configured to code an intra prediction mode inaccordance with the techniques of this disclosure. Additionally oralternatively, entropy encoding unit 56 may be configured to determinecontext information for CABAC coding using the techniques of thisdisclosure.

For example, assuming that motion compensation unit 44 elects to performmerge mode, motion compensation unit 44 may form a candidate listincluding a set of merge candidates. Motion compensation unit 44 may addcandidates to the candidate list based on a particular, predeterminedorder. Motion compensation unit 44 may also add additional candidatesand perform pruning of the candidate list and prioritize the candidatelist, as discussed above. Ultimately, mode select unit 40 may determinewhich of the candidates is to be used to encode motion information ofthe current block, and encode a merge index representing the selectedcandidate.

Intra-prediction unit 46 may intra-predict a current block, as analternative to the inter-prediction performed by motion estimation unit42 and motion compensation unit 44, as described above. In particular,intra-prediction unit 46 may determine an intra-prediction mode to useto encode a current block. In some examples, intra-prediction unit 46may encode a current block using various intra-prediction modes, e.g.,during separate encoding passes, and intra-prediction unit 46 (or modeselect unit 40, in some examples) may select an appropriateintra-prediction mode to use from the tested modes.

For example, intra-prediction unit 46 may calculate rate-distortionvalues using a rate-distortion analysis for the various testedintra-prediction modes, and select the intra-prediction mode having thebest rate-distortion characteristics among the tested modes.Rate-distortion analysis generally determines an amount of distortion(or error) between an encoded block and an original, unencoded blockthat was encoded to produce the encoded block, as well as a bitrate(that is, a number of bits) used to produce the encoded block.Intra-prediction unit 46 may calculate ratios from the distortions andrates for the various encoded blocks to determine which intra-predictionmode exhibits the best rate-distortion value for the block.

After selecting an intra-prediction mode for a block, intra-predictionunit 46 may provide information indicative of the selectedintra-prediction mode for the block to entropy encoding unit 56. Entropyencoding unit 56 may encode the information indicating the selectedintra-prediction mode. As discussed above, intra prediction unit 46and/or entropy encoding unit 56 may use the techniques of thisdisclosure to encode the information indicating the selectedintra-prediction mode. In particular, entropy encoding unit 56 maydetermine one or more most probable modes from neighboring blocks to theblock based on geometry information, e.g., distances betweenrepresentative points of the block and the neighboring blocks. Entropyencoding unit 56 may further entropy encode data indicating whether theintra prediction mode used to intra predict the block is one of the mostprobable modes, or a different mode, and if a different mode, an indexinto a list of intra prediction modes excluding the most probable modes.

Video encoder 20 may include in the transmitted bitstream configurationdata, which may include a plurality of intra-prediction mode indextables and a plurality of modified intra-prediction mode index tables(also referred to as codeword mapping tables), definitions of encodingcontexts for various blocks, and indications of a most probableintra-prediction mode, an intra-prediction mode index table, and amodified intra-prediction mode index table to use for each of thecontexts.

Video encoder 20 forms a residual video block by subtracting theprediction data from mode select unit 40 from the original video blockbeing coded. Summer 50 represents the component or components thatperform this subtraction operation. Transform processing unit 52 appliesa transform, such as a discrete cosine transform (DCT) or a conceptuallysimilar transform, to the residual block, producing a video blockcomprising residual transform coefficient values. Transform processingunit 52 may perform other transforms which are conceptually similar toDCT. Wavelet transforms, integer transforms, sub-band transforms orother types of transforms could also be used.

In any case, transform processing unit 52 applies the transform to theresidual block, producing a block of residual transform coefficients.The transform may convert the residual information from a pixel valuedomain to a transform domain, such as a frequency domain. Transformprocessing unit 52 may send the resulting transform coefficients toquantization unit 54. Quantization unit 54 quantizes the transformcoefficients to further reduce bit rate. The quantization process mayreduce the bit depth associated with some or all of the coefficients.The degree of quantization may be modified by adjusting a quantizationparameter. In some examples, quantization unit 54 may then perform ascan of the matrix including the quantized transform coefficients.Alternatively, entropy encoding unit 56 may perform the scan.

Following quantization, entropy encoding unit 56 entropy codes thequantized transform coefficients. For example, entropy encoding unit 56may perform context adaptive variable length coding (CAVLC), contextadaptive binary arithmetic coding (CABAC), syntax-based context-adaptivebinary arithmetic coding (SBAC), probability interval partitioningentropy (PIPE) coding or another entropy coding technique. In the caseof context-based entropy coding, context may be based on neighboringblocks. Following the entropy coding by entropy encoding unit 56, theencoded bitstream may be transmitted to another device (e.g., videodecoder 30) or archived for later transmission or retrieval.

Entropy encoding unit 56 may use geometry information may be used forthe determination of context information for CABAC coding. For example,when CABAC coding values for syntax elements of a block, entropyencoding unit 56 may determine one or more neighboring blocks to theblock from which to retrieve information to be used to form the contextinformation based on geometry information, e.g., distances betweenrepresentative points of the block and the neighboring blocks. In someexamples, entropy encoding unit 56 may weight the contributions of datafrom two or more neighboring blocks according to the geometryinformation, as discussed above.

Inverse quantization unit 58 and inverse transform unit 60 apply inversequantization and inverse transformation, respectively, to reconstructthe residual block in the pixel domain, e.g., for later use as areference block. Motion compensation unit 44 may calculate a referenceblock by adding the residual block to a predictive block of one of theframes of reference picture memory 64. Motion compensation unit 44 mayalso apply one or more interpolation filters to the reconstructedresidual block to calculate sub-integer pixel values for use in motionestimation. Summer 62 adds the reconstructed residual block to themotion compensated prediction block produced by motion compensation unit44 to produce a reconstructed video block for storage in referencepicture memory 64. The reconstructed video block may be used by motionestimation unit 42 and motion compensation unit 44 as a reference blockto inter-code a block in a subsequent video frame.

FIG. 16 is a block diagram illustrating an example of video decoder 30that may be configured to perform the motion vector predictiontechniques of this disclosure. In the example of FIG. 16, video decoder30 includes an entropy decoding unit 70, motion compensation unit 72,intra prediction unit 74, inverse quantization unit 76, inversetransformation unit 78, reference picture memory 82 and summer 80. Videodecoder 30 may, in some examples, perform a decoding pass generallyreciprocal to the encoding pass described with respect to video encoder20 (FIG. 15). Motion compensation unit 72 may generate prediction databased on motion vectors received from entropy decoding unit 70, whileintra-prediction unit 74 may generate prediction data based onintra-prediction mode indicators received from entropy decoding unit 70.

During the decoding process, video decoder 30 receives an encoded videobitstream that represents video blocks of an encoded video slice andassociated syntax elements from video encoder 20. Entropy decoding unit70 of video decoder 30 entropy decodes the bitstream to generatequantized coefficients, motion vectors or intra-prediction modeindicators, and other syntax elements. In some examples, entropydecoding unit 70 may use the techniques of this disclosure to determinecontext information for entropy decoding values of syntax elements. Forexample, entropy decoding unit 70 may determine one or more neighboringblocks (and in some examples, weights) using geometry information (e.g.,distances between a representative point of a current block andrepresentative points of the neighboring blocks) to determine contextinformation to be used to CABAC decode values of syntax elements for thecurrent block. Entropy decoding unit 70 forwards the motion vectors andother syntax elements to motion compensation unit 72. Video decoder 30may receive the syntax elements at the video slice level and/or thevideo block level.

When the video slice is coded as an intra-coded (I) slice, intraprediction unit 74 may generate prediction data for a video block of thecurrent video slice based on a signaled intra prediction mode and datafrom previously decoded blocks of the current frame or picture. When thevideo frame is coded as an inter-coded (i.e., B, P or GPB) slice, motioncompensation unit 72 produces predictive blocks for a video block of thecurrent video slice based on the motion vectors and other syntaxelements received from entropy decoding unit 70. The predictive blocksmay be produced from one of the reference pictures within one of thereference picture lists. Video decoder 30 may construct the referenceframe lists, List 0 and List 1, using default construction techniquesbased on reference pictures stored in reference picture memory 82.

Motion compensation unit 72 may form candidate lists, e.g., whendecoding motion vectors using merge mode or AMVP mode, using geometryinformation between the current block and the neighboring blocks todetermine the priority or insertion order for the construction ofcandidate lists such as a merge candidate list or an AMVP candidatelist. Additionally or alternatively, intra prediction unit 74 maydetermine one or more most probable modes for intra prediction (wherethe most probable modes correspond to a candidate list) using geometryinformation between the current block and the neighboring blocks todetermine the priority or insertion order for the most probable modes.In one example, the distance between a representative point of a currentblock and a representative point of the neighboring block is used as thegeometry information to determine the priority or insertion order forthe construction of the candidate lists. In one example, the shorterdistance between that candidate's representative point and currentrepresentative point has higher priority, or vice versa. In anotherexample, the distance can be LN-norm distance (N can be 1, 2 or anyother positive integer).

Motion compensation unit 72 determines prediction information for avideo block of the current video slice by parsing the motion vectors andother syntax elements, and uses the prediction information to producethe predictive blocks for the current video block being decoded. Forexample, motion compensation unit 72 uses some of the received syntaxelements to determine a prediction mode (e.g., intra- orinter-prediction) used to code the video blocks of the video slice, aninter-prediction slice type (e.g., B slice, P slice, or GPB slice),construction information for one or more of the reference picture listsfor the slice, motion vectors for each inter-encoded video block of theslice, inter-prediction status for each inter-coded video block of theslice, and other information to decode the video blocks in the currentvideo slice.

Motion compensation unit 72 may also perform interpolation based oninterpolation filters. Motion compensation unit 72 may use interpolationfilters as used by video encoder 20 during encoding of the video blocksto calculate interpolated values for sub-integer pixels of referenceblocks. In this case, motion compensation unit 72 may determine theinterpolation filters used by video encoder 20 from the received syntaxelements and use the interpolation filters to produce predictive blocks.

Video decoder 30 may be configured to perform any of the varioustechniques of this disclosure discussed above with respect to FIG. 14,and as will be discussed in more detail below. For example, motioncompensation unit 72 may be configured to determine to perform motionvector prediction using AMVP or merge mode in accordance with thetechniques of this disclosure. Entropy decoding unit 70 may decode oneor more syntax elements representing how motion information is coded forthe current block.

Assuming that the syntax elements indicate that merge mode is performed,motion compensation unit 72 may form a candidate list including a set ofmerge candidates. Motion compensation unit 72 may add candidates to thecandidate list based on a particular, predetermined order. Motioncompensation unit 72 may also add additional candidates and performpruning of the candidate list, as discussed above. Ultimately, motioncompensation unit 72 may decode a merge index representing which of thecandidates is used to code motion information for the current block.

Inverse quantization unit 76 inverse quantizes, i.e., de-quantizes,quantized transform coefficients provided in the bitstream and entropydecoded by entropy decoding unit 70. The inverse quantization processmay include use of a quantization parameter QP_(Y) calculated by videodecoder 30 for each video block in the video slice to determine a degreeof quantization and, likewise, a degree of inverse quantization thatshould be applied.

Inverse transform unit 78 applies an inverse transform, e.g., an inverseDCT, an inverse integer transform, or a conceptually similar inversetransform process, to the transform coefficients in order to produceresidual blocks in the pixel domain.

After motion compensation unit 72 generates the predictive block for thecurrent video block based on the motion vectors and other syntaxelements, video decoder 30 forms a decoded video block by summing theresidual blocks from inverse transform unit 78 with the correspondingpredictive blocks generated by motion compensation unit 72. Summer 80represents the component or components that perform this summationoperation. If desired, a deblocking filter may also be applied to filterthe decoded blocks in order to remove blockiness artifacts. Other loopfilters (either in the coding loop or after the coding loop) may also beused to smooth pixel transitions, or otherwise improve the videoquality. The decoded video blocks in a given frame or picture are thenstored in reference picture memory 82, which stores reference picturesused for subsequent motion compensation. Reference picture memory 82also stores decoded video for later presentation on a display device,such as display device 32 of FIG. 14.

FIG. 17 is a flowchart illustrating an example method of encoding videodata according to the techniques of this disclosure. For purposes ofexample and explanation, the method of FIG. 17 is explained as beingperformed by video encoder 20 of FIG. 15. However, it should beunderstood that other devices may be configured to perform this or asimilar method.

Initially, video encoder 20 receives a current block to be encoded(300). Mode select unit 40 then determines a prediction mode to be usedto predict the current block (302). For example, mode select unit 40 mayinitially determine whether to use an intra-prediction mode or aninter-prediction mode. If mode select unit 40 determines to useintra-prediction, mode select unit 40 may further determine one of avariety of intra-prediction modes (e.g., a directional mode, DC mode,planar mode, or the like) to be used to predict the current block. Ifmode select unit 40 determines to use inter-prediction mode, motionestimation unit 42 may perform a motion search to determine a motionvector for one or more prediction units (PUs) of the current block.

In any case, video encoder 20 may predict the current block using theprediction mode (304). For example, in inter-prediction mode, motioncompensation unit 44 may use the motion vector determined by motionestimation unit 42 to calculate a predicted block for the current block.As another example, in intra-prediction mode, intra-prediction unit 46may generate the predicted block using values of neighboring pixels tothe current block according to the determined intra-prediction mode.

Video encoder 20 may then determine distances between a representativepoint of the current block and representative points of neighboringblocks (306), such as spatial and/or temporal neighboring blocks. Therepresentative points may correspond to, for example, center points ofthe blocks (e.g., as shown in FIGS. 12 and 13), or other representativepoints, such as top-left points of the blocks. The neighboring blocksmay correspond to coding units, PUs, or sub-PUs, as discussed above.

Video encoder 20 then adds data from one or more of the neighboringblocks to a candidate list according to the determined distances (308).For example, for intra-prediction, video encoder 20 may determine a listof one or more most probable intra-prediction modes from the neighboringblocks, e.g., the intra-prediction modes used to predict the neighboringblocks having the shortest distances, where these blocks may be referredto as candidates included in the candidate list. As another example, forinter-prediction, video encoder 20 may form a candidate list of mergemode or AMVP mode for encoding a motion vector.

In any case, entropy encoding unit 56 may encode prediction informationusing the candidate list (310). For example, for intra-prediction,entropy encoding unit 56 may encode a syntax element representingwhether, and which of, the most probable modes are used to predict thecurrent block. If none of the most probable modes is used to predict thecurrent block, entropy encoding unit 56 may further encode informationrepresenting which of a remaining set of intra-prediction modes is usedto predict the current block. As another example, for inter-prediction,entropy encoding unit 56 may encode motion information according tomerge mode or AMVP mode. For example, for merge mode, entropy encodingunit 56 may entropy encode an index into the candidate list. As anotherexample, for AMVP mode, entropy encoding unit 56 may entropy encode anindex into the candidate list, motion vector difference information, areference picture list identifier, and an index into the referencepicture list.

Video encoder 20 may also calculate a residual block for the currentblock (312). That is, as discussed above, summer 50 may calculatepixel-by-pixel differences between the predicted block and the originalcurrent block to calculate the residual block. Transform processing unit52 may then transform the pixel differences of the residual block fromthe pixel domain (or spatial domain) to the frequency domain to producetransform coefficients, and quantization unit 54 may then quantize thetransform coefficients, to thereby transform and quantize the residualblock (314). Entropy encoding unit 56 may then entropy encode thequantized transform coefficients (316).

Although not shown in the example of FIG. 17, a method including stepssimilar to those of steps 306-310 may additionally or alternatively beused by entropy encoding unit 56 to entropy encode values for one ormore syntax elements of a current block of video data. Such syntaxelements may include, for example, any or all of a coding unittransquant bypass flag, a coding unit skip flag, a coded block flag, aprediction mode flag, a residual quadtree transform root coded blockflag, a merge index, a merge flag, a coded block flag for a luminanceblock, or a coded block flag for a chrominance block. In general, such amethod may include determining distances to neighboring blocks for thepurpose of determining context information for CABAC coding. Entropyencoding unit 56 may use the context information to initialize and/orupdate a context model representing a probability of a bit of abinarized value having a value equal to a most probable symbol or aleast probable symbol.

In this manner, the method of FIG. 17 represents an example of a methodof coding video data including determining a plurality of distancesbetween a first representative point of a current block of video dataand a plurality of second representative points of neighboring blocks tothe current block, adding one or more of the neighboring blocks ascandidates to a candidate list of the current block in an orderaccording to the distances between the first representative point andthe second representative points, and coding (specifically, encoding, inthis example) the current block using the candidate list.

FIG. 18 is a flowchart illustrating an example method of decoding videodata in accordance with the techniques of this disclosure. For purposesof example and explanation, the method of FIG. 18 is explained as beingperformed by video decoder 30 of FIG. 16. However, it should beunderstood that other devices may be configured to perform this or asimilar method.

Initially, in this example, video decoder 30 receives a current block tobe decoded (330). The current block may be, for example, a coding unit(CU), a prediction unit (PU), a portion of a CU corresponding to a PU, acollection of sub-PUs, or the like. In accordance with the techniques ofthis disclosure, video decoder 30 determines geometry information, i.e.,distances between a representative point of the current block andrepresentative points of neighboring blocks to the current block (332).The representative points may be, for example, centers of the blocks,top-left corners of the blocks, or the like. The neighboring blocks maybe PUs or sub-PUs, in some examples. Furthermore, the neighboring blocksmay be spatial and/or temporal neighbors.

Video decoder 30 then adds data from the neighboring blocks to acandidate list according to the determined distances (334). Thedistances may generally represent priorities for ordering of the data inthe candidate list, where shorter distances may generally representhigher priorities. As discussed above, the candidate list may be acandidate list of merge mode or AMVP mode decoding of a motion vector ifthe current block is inter-predicted, or a list of one or more mostprobable modes if the current block is intra-predicted. Video decoder 30also determines the prediction mode (338), e.g., either inter- orintra-prediction, and predicts the block according to the predictionmode using the candidate list (340). In particular, if the predictionmode is intra-prediction, intra-prediction unit 74 determines an actualintra mode to be used to predict the block based on whether dataindicates that one of the most probable modes is used, and if not, anidentifier of the actual prediction mode. On the other hand, if theprediction mode is inter-prediction, motion compensation unit 72 maydecode a motion vector for the current block according to merge mode orAMVP mode and generate a predicted block using the motion vector byretrieving data identified by the motion vector from reference picturememory 82.

Additionally, entropy decoding unit 70 entropy decodes quantizedtransform coefficients of the current block (342). Inverse quantizationunit 76 inverse quantizes quantized transform coefficients for thecurrent block, and inverse transform unit 78 applies an inversetransform to the transform coefficients, thereby inverse quantizing andinverse transforming the quantized transform coefficients (344), toproduce a residual block. Summer 80 then adds values of the residualblock with values of the predicted block on a pixel-by-pixel basis todecode the current block (346).

Again it should be understood that video decoder 30 may apply a methodincluding steps similar to steps 332-336 of FIG. 18 when performingentropy decoding of values of various syntax elements, in some examples.Such syntax elements may include, for example, any or all of a codingunit transquant bypass flag, a coding unit skip flag, a coded blockflag, a prediction mode flag, a residual quadtree transform root codedblock flag, a merge index, a merge flag, a coded block flag for aluminance block, or a coded block flag for a chrominance block. Ingeneral, such a method may include determining distances to neighboringblocks for the purpose of determining context information for CABACcoding. Entropy decoding unit 70 may use the context information toinitialize and/or update a context model representing a probability of abit of a binarized value having a value equal to a most probable symbolor a least probable symbol.

In this manner, the method of FIG. 18 represents an example of a methodof coding video data including determining a plurality of distancesbetween a first representative point of a current block of video dataand a plurality of second representative points of neighboring blocks tothe current block, adding one or more of the neighboring blocks ascandidates to a candidate list of the current block in an orderaccording to the distances between the first representative point andthe second representative points, and coding (specifically, decoding, inthis example) the current block using the candidate list.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablegate arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of coding video data, the methodcomprising: determining a plurality of distances between a firstrepresentative point of a current block of video data and a plurality ofsecond representative points of neighboring blocks to the current block;adding one or more of the neighboring blocks as candidates to acandidate list of the current block in an order according to thedistances between the first representative point and the secondrepresentative points; and coding the current block using the candidatelist.
 2. The method of claim 1, wherein the candidate list comprises oneof a merge candidate list, an advanced motion vector prediction (AMVP)candidate list, or an intra most probable mode (MPM) list.
 3. The methodof claim 2, wherein the candidate list comprises the merge candidatelist, and wherein coding the current block comprises coding motioninformation for the current block according to merge mode using acandidate of the merge candidate list.
 4. The method of claim 2, whereinthe candidate list comprises the AMVP candidate list, and wherein codingthe current block comprises coding motion information for the currentblock according to AMVP mode using a candidate of the AMVP candidatelist.
 5. The method of claim 2, wherein the candidate list comprises theintra MPM list, and wherein coding the current block comprises coding anindication of an intra-prediction mode used to intra-predict the currentblock using the intra MPM list, and intra-predicting the current blockusing the intra-prediction mode.
 6. The method of claim 1, wherein atleast one of the neighboring blocks comprises a sub-prediction unit(sub-PU), and wherein the one of the second representative pointsassociated with the sub-PU comprises a center point of the sub-PU. 7.The method of claim 1, wherein the first representative point of thecurrent block comprises a center point of the current block and thesecond representative points of the neighboring blocks compriserespective center points of the neighboring blocks.
 8. The method ofclaim 1, wherein the first representative point of the current blockcomprises a top-left point of the current block and the secondrepresentative points of the neighboring blocks comprise respectivetop-left points of the neighboring blocks.
 9. The method of claim 1,wherein the neighboring blocks comprise one or more of spatiallyneighboring blocks to the current block or temporally neighboring blocksto the current block.
 10. The method of claim 1, wherein the candidatelist comprises a list of candidates from which to determine contextinformation for context-adaptive binary arithmetic coding (CABAC) of avalue for a syntax element of the current block, and wherein coding thecurrent block comprises CABAC coding the value for the syntax element ofthe current block using the context information determined from the listof candidates.
 11. The method of claim 10, wherein the syntax elementcomprises one of a coding unit transquant bypass flag, a coding unitskip flag, a coded block flag, a prediction mode flag, a residualquadtree transform root coded block flag, a merge index, a merge flag, acoded block flag for a luminance block, or a coded block flag for achrominance block.
 12. The method of claim 10, further comprisingdetermining the context information, comprising weighting contributionsof values from the neighboring blocks according to the distances betweenthe first representative point and the second representative points. 13.The method of claim 1, wherein coding comprises encoding the currentblock using the candidate list.
 14. The method of claim 1, whereincoding comprises decoding the current block using the candidate list.15. A device for coding video data, the device comprising: a memoryconfigured to store the video data; and one or more processorsimplemented in circuitry and configured to: determine a plurality ofdistances between a first representative point of a current block ofvideo data and a plurality of second representative points ofneighboring blocks to the current block; add one or more of theneighboring blocks as candidates to a candidate list of the currentblock in an order according to the distances between the firstrepresentative point and the second representative points; and code thecurrent block using the candidate list.
 16. The device of claim 15,wherein the candidate list comprises one of a merge candidate list, anadvanced motion vector prediction (AMVP) candidate list, or an intramost probable mode (MPM) list.
 17. The device of claim 15, wherein atleast one of the neighboring blocks comprises a sub-prediction unit(sub-PU), and wherein the one of the second representative pointsassociated with the sub-PU comprises a center point of the sub-PU. 18.The device of claim 15, wherein the first representative point of thecurrent block comprises a center point of the current block and thesecond representative points of the neighboring blocks compriserespective center points of the neighboring blocks.
 19. The device ofclaim 15, wherein the candidate list comprises a list of candidates fromwhich to determine context information for context-adaptive binaryarithmetic coding (CABAC) of a value for a syntax element of the currentblock, and wherein the one or more processors are configured to CABACcode the value for the syntax element of the current block using thecontext information determined from the list of candidates.
 20. Thedevice of claim 15, wherein the device comprises one of a video encoderconfigured to encode the current block or a video decoder configured todecode the current block.
 21. A device for coding video data, the devicecomprising: means for determining a plurality of distances between afirst representative point of a current block of video data and aplurality of second representative points of neighboring blocks to thecurrent block; means for adding one or more of the neighboring blocks ascandidates to a candidate list of the current block in an orderaccording to the distances between the first representative point andthe second representative points; and means for coding the current blockusing the candidate list.
 22. The device of claim 21, wherein thecandidate list comprises one of a merge candidate list, an advancedmotion vector prediction (AMVP) candidate list, or an intra mostprobable mode (MPM) list.
 23. The device of claim 21, wherein at leastone of the neighboring blocks comprises a sub-prediction unit (sub-PU),and wherein the one of the second representative points associated withthe sub-PU comprises a center point of the sub-PU.
 24. The device ofclaim 21, wherein the first representative point of the current blockcomprises a center point of the current block and the secondrepresentative points of the neighboring blocks comprise respectivecenter points of the neighboring blocks.
 25. The device of claim 21,wherein the candidate list comprises a list of candidates from which todetermine context information for context-adaptive binary arithmeticcoding (CABAC) of a value for a syntax element of the current block, andwherein the means for coding the current block comprise means for CABACcoding the value for the syntax element of the current block using thecontext information determined from the list of candidates.
 26. Acomputer-readable storage medium having stored thereon instructionsthat, when executed, cause a processor to: determine a plurality ofdistances between a first representative point of a current block ofvideo data and a plurality of second representative points ofneighboring blocks to the current block; add one or more of theneighboring blocks as candidates to a candidate list of the currentblock in an order according to the distances between the firstrepresentative point and the second representative points; and code thecurrent block using the candidate list.
 27. The computer-readablestorage medium of claim 26, wherein the candidate list comprises one ofa merge candidate list, an advanced motion vector prediction (AMVP)candidate list, or an intra most probable mode (MPM) list.
 28. Thecomputer-readable storage medium of claim 26, wherein at least one ofthe neighboring blocks comprises a sub-prediction unit (sub-PU), andwherein the one of the second representative points associated with thesub-PU comprises a center point of the sub-PU.
 29. The computer-readablestorage medium of claim 26, wherein the first representative point ofthe current block comprises a center point of the current block and thesecond representative points of the neighboring blocks compriserespective center points of the neighboring blocks.
 30. Thecomputer-readable storage medium of claim 26, wherein the candidate listcomprises a list of candidates from which to determine contextinformation for context-adaptive binary arithmetic coding (CABAC) of avalue for a syntax element of the current block, and wherein theinstructions that cause the processor to code the current block compriseinstructions that cause the processor to CABAC code the value for thesyntax element of the current block using the context informationdetermined from the list of candidates.